3D inside PDFs
3D models in PDF
Montecristo reads the U3D and PRC models embedded in technical datasheets, CAD exports and scientific papers, and draws them in an OpenGL viewer on the page. Full variant only.
PDF reader · Linux & Windows
Montecristo
Opens PDF, EPUB, XPS, CBZ, FB2 and SVG. On PDFs it writes standard annotations, fills in forms, sets passwords and checks digital signatures, and it shows the 3D models (U3D and PRC) embedded in them.
U3D and PRC models embedded in PDFs, on Linux and Windows
- 6
- formats: PDF, EPUB, XPS, CBZ, FB2, SVG
- 14
- standard PDF annotation types
- 0
- telemetry, accounts or ads
- 2
- platforms: Linux and Windows 10/11
What it does
Main functions
3D models inside PDFs, forms with calculations, and reading long documents. Annotating, protecting and searching have a toolbar each, just below.
Forms with calculations
Fills text fields (also multi-line and comb), checkboxes, radio buttons, drop-down menus and lists on the page, with Tab to move between fields. Field scripts for validation, calculation and formatting run unless you turn them off in Settings. It fills existing forms; it does not create them or send them anywhere.
Long documents
Pages are rendered on their own thread, so the window does not wait for them to draw. The pages around the one you are reading are prepared in advance. A clickable outline lists the sections, and search counts every match.
3D viewer
Rotate and zoom with the mouse
An engine assembly open in the PDF: drag to rotate, scroll to zoom.
Three toolbars
Annotate, Protect, Search
One toolbar is open at a time. Each opens from the header and closes the same way.
Annotate · Ctrl+Shift+A
Annotations
Highlight, underline and strike out text, draw with the pen, add notes, shapes and images. Every mark is a standard PDF annotation; a watermark is written into the page content when you save. Save appends the changes to the end of the same file; Save As writes a copy. With the Select tool you pick one mark or several (Shift+click), move them, also to another page, and delete, copy, paste, duplicate or rotate them by 90°.
Protect
Passwords, Undercover, signatures
Set a password and save an AES-256 encrypted copy, with a strength estimate in bits as you type. Undercover (Ctrl+Shift+N) blurs and darkens the page except around the pointer, 3D views and form and note editors included. Digital signatures are checked when a document opens. Password-protected PDFs open when you type the password; their print, copy and edit restrictions are not enforced.
Search · Ctrl+F
Search
Searches the document and counts every match. Options: match case, whole words, or a regular expression. It can also search the text of notes and the values of form fields.
The 3D viewer
Viewing 3D models in PDFs
Rotate, pan, zoom
Drag to rotate, scroll to zoom, switch to pan from the toolbar. A zoom indicator shows the current scale.
Preset views
The default view (first button of the toolbar), X, Y, Z and isometric views, plus the views saved in the PDF. Changing view is animated.
Ten render modes
A menu in the 3D toolbar lists them: shaded, solid, transparent, four kinds of wireframe, two of vertices, bounding box.
Colors, materials, textures
The model is drawn with the colors, materials and textures stored in the file. The light can be switched on or off.
Component tree
The model's parts are listed in a tree. Select one (or click it on the model), right-click, and isolate it or hide it; Show all brings everything back. A data sheet gives each part's name, triangle count, dimensions and volume. The model can be exported as .u3d or .prc.
Design
How it is built
How the program renders, what its interface is made of, and what it does not do on the network.
01
Rendering
Pages are rendered on a separate thread, so the window does not wait for them to draw. The rendering engine is native code, not a web page in a window. “Save memory on long documents” frees the pages you have scrolled past, and the Performance window shows memory and rendered pages for each tab.
02
Native interface
A GTK 4 interface on Linux. On Windows, the same program uses the system title bar and window snapping. It is not an Electron app or a web wrapper.
03
Network and privacy
No telemetry, no accounts, no ads and no automatic updates. The only network request is the signature revocation check of the Full variant, which Settings › Security turns off; Minimal and Safe contain no network code. Settings and the list of recent documents are kept on your computer and can be erased from Settings › Security; the Safe variant keeps no such list.
Other functions
Multiple tabs
Several documents in one window. Drag files in: each opens its own tab, and a file that is already open is not opened twice. A tab dragged out of the window becomes a window of its own.
Other formats
Also opens EPUB, XPS and OpenXPS, CBZ comics, FictionBook and SVG, in the same interface. Annotations, forms and passwords apply to PDFs only.
Search and selection
Ctrl+F opens the search toolbar. Select text with the mouse and copy it; in Windows 0.3.10 a double-click selects a word.
Outline and links
Clickable side outline, links inside the document and to other documents. Web addresses open in the system browser, after you confirm.
Images on the page
Right-click an image on the page: copy it, save it, or read its EXIF data (JPEG only).
Watermark
Adds a text watermark with the font, color, opacity, rotation and page range you choose, once per page or repeated across it (sparse, medium or dense). Until you save it can be changed or removed; on saving, after you confirm, it is written into the page content, so it can no longer be selected or moved and shows in any PDF reader.
Source view
The PDF as indented text, editable object by object and saved incrementally.
Zoom and rotation
Zoom from 10% to 6400% so even the tiny pages of some 3D PDFs fill the window; fit width or page, Ctrl+wheel zoom, page rotation, middle-button pan. Continuous, single and double-page layouts. In Windows 0.3.10, full screen shows only the document.
Digital signatures
Checks the signatures on documents you receive: unchanged or altered, trusted or not, and what was added after signing. EU qualified signatures are recognised through the EU trusted lists built into the program. It does not create signatures. How verification works.
English and Italian
The interface is available in English and Italian only.
Built-in fonts
Fonts embedded in a PDF are drawn as stored. For fonts that are only named, Montecristo uses fonts built into the program. It does not read the fonts installed on the computer and does not download any.
The 14 PDF standard fonts
Nimbus Sans, Nimbus Roman and Nimbus Mono PS in regular, bold, italic and bold italic, plus Standard Symbols PS and Dingbats. They stand in for Helvetica, Times, Courier, Symbol and ZapfDingbats.
Books
Charis SIL in four styles, the default text face for EPUB and FictionBook.
Chinese, Japanese, Korean
Droid Sans Fallback.
Symbols, math, music, emoji
Noto Sans Symbols and Symbols2 (with Braille), Noto Sans Math, Noto Music and Noto Emoji, in black and white.
Over 150 writing systems
Noto Serif for Latin, Greek and Cyrillic, Noto Naskh Arabic and Noto Nastaliq Urdu, and one Noto font for each of 149 more scripts.
Show all 149 scripts
- Adlam
- Ahom
- Anatolian Hieroglyphs
- Armenian
- Avestan
- Balinese
- Bamum
- Bassa Vah
- Batak
- Bengali
- Bhaiksuki
- Brahmi
- Buginese
- Buhid
- Canadian Aboriginal
- Carian
- Caucasian Albanian
- Chakma
- Cham
- Cherokee
- Chorasmian
- Coptic
- Cuneiform
- Cypriot
- Cypro-Minoan
- Deseret
- Devanagari
- Dives Akuru
- Dogra
- Duployan
- Egyptian Hieroglyphs
- Elbasan
- Elymaic
- Ethiopic
- Georgian
- Glagolitic
- Gothic
- Grantha
- Gujarati
- Gunjala Gondi
- Gurmukhi
- Hanifi Rohingya
- Hanunó’o
- Hatran
- Hebrew
- Imperial Aramaic
- Inscriptional Pahlavi
- Inscriptional Parthian
- Javanese
- Kaithi
- Kannada
- Kawi
- Kayah Li
- Kharoshthi
- Khitan Small Script
- Khmer
- Khojki
- Khudawadi
- Lao
- Lepcha
- Limbu
- Linear A
- Linear B
- Lisu
- Lycian
- Lydian
- Mahajani
- Makasar
- Malayalam
- Mandaic
- Manichaean
- Marchen
- Masaram Gondi
- Medefaidrin
- Meetei Mayek
- Mende Kikakui
- Meroitic
- Miao
- Modi
- Mongolian
- Mro
- Multani
- Myanmar
- Nabataean
- Nag Mundari
- Nandinagari
- Newa
- New Tai Lue
- N’Ko
- Nushu
- Nyiakeng Puachue Hmong
- Ogham
- Ol Chiki
- Old Hungarian
- Old Italic
- Old North Arabian
- Old Permic
- Old Persian
- Old Sogdian
- Old South Arabian
- Old Turkic
- Old Uyghur
- Oriya
- Osage
- Osmanya
- Pahawh Hmong
- Palmyrene
- Pau Cin Hau
- Phags-pa
- Phoenician
- Psalter Pahlavi
- Rejang
- Runic
- Samaritan
- Saurashtra
- Sharada
- Shavian
- Siddham
- Sinhala
- Sogdian
- Sora Sompeng
- Soyombo
- Sundanese
- Sunuwar
- Syloti Nagri
- Syriac
- Tagalog
- Tagbanwa
- Tai Le
- Tai Tham
- Tai Viet
- Takri
- Tamil
- Tangsa
- Telugu
- Thaana
- Thai
- Tibetan
- Tifinagh
- Tirhuta
- Toto
- Ugaritic
- Vai
- Vithkuqi
- Wancho
- Warang Citi
- Yezidi
- Yi
- Zanabazar Square
Digital signatures EU trusted lists built in
Signature checking: integrity and trust
Montecristo checks the signatures on the PDFs you receive and reports what it could prove: whether the content changed, and whether the signer is trusted. It is in the Windows and Linux downloads below, all three variants. It does not create signatures.
Has the document changed?
That's integrity. A signature seals a fingerprint of the content: change one character and it no longer matches. The check is computed on your computer.
Is the signer who they claim to be?
That's trust, and it isn't in the PDF: anyone can make a certificate with any name. Montecristo never calls a signature trusted when it has only checked that the document is intact.
Trusted certificates
A signer counts as trusted when their certificate leads back to one you have put in the trusted certificates folder (Protect bar → Open the trusted certificates folder; .pem, .crt or .cer files). The app never downloads or installs certificates by itself, and it doesn't use your system's certificates, which are meant for websites. A signer also counts as trusted when their certificate leads back to a qualified certificate authority of the EU national trusted lists (eIDAS; Italy's is published by AgID), which are built into the program: 872 certificate authorities and 1,078 timestamping authorities from 30 of the 31 national lists (Latvia's could not be downloaded). The lists were verified when this version was built and the panel shows their date. Outside the EU, trust comes only from the folder. Which certificates?
Limit
For a signer whose authority is neither in your folder nor in the built-in EU lists, the most Montecristo can say is: unchanged, but it can't confirm who signed. Outside the EU there is no open official list to build on at all.
The five results
Signed, trusted
Unchanged since signing, and the signer's certificate leads back to one you trust.
Signed, not trusted
Unchanged, but the certificate doesn't lead to one you trust, is self-signed, or has expired or been revoked with no timestamp proving the signature came first. If the signer matters, confirm another way.
Signature not verifiable
A format Montecristo can't read yet, or a file too damaged for a reliable check. Not a judgement on the document.
Signed, changed afterwards
The signed part is intact, but something was added later in a way the signature doesn't allow (new text on a page, pages added or removed), or content was added that Montecristo couldn't classify. What's on screen is not what was signed.
Signature altered
The signed content no longer matches its signature. Don't rely on this document.
Changes after signing.
Normal
Proof that a certificate wasn't revoked, added for long-term signatures (PAdES-LT); another signature; filled-in form fields; comments, unless the signer ruled them out. Montecristo says so in one line and doesn't mark the document as changed.
Not normal
Text added to a page, pages added or removed, the signature's details rewritten, scripts added. Anything Montecristo can't classify counts as not allowed.
Notes added later
A comment or stamp added after signing can be allowed and still cover the signed text. Montecristo tells you annotations were added and asks you to check them; it doesn't list them one by one.
Revocation, timestamps and the panel
Revoked certificates
A certificate can be cancelled before it expires. Montecristo first reads the revocation proof the document carries. When there is none, the Full variant asks the authority that issued the certificate (OCSP, or its revocation list); the authority sees your IP address and which certificate is checked. This is on by default; in Settings › Security, Check signatures online turns it off, and turning off Check online automatically limits it to a Check online button in the Protect bar. Only plain web addresses on the public internet are contacted, never your local network. Minimal and Safe never go online: with no proof inside the document, revocation is not known. The panel says where the answer came from.
Timestamps and dates
A timestamp proves when a document was signed, so an old signature whose certificate has since expired can still be good. The timestamp authority has to be one you trust too. Without a timestamp, the date shown is the one the signer declared, and the panel says so.
The panel in the app
Open the Protect bar on a signed document: one row per signature with who signed, when, what was established and why it isn't trusted. Show on page scrolls to the signature, and while the bar is open every visible signature gets a frame in its verdict's colour. Documents without signatures show nothing. When trust comes from the built-in EU list, the panel says so, and it shows the date of the list; after six months it suggests installing a newer version.
Download
Full, Minimal and Safe builds
Three editions of the same program. They differ in which code is compiled in; the table below lists what each one contains.
Full
All features
Everything the program does: 3D models (U3D and PRC), forms with field scripts, the annotation tools, Protected Mode, signature checking (with the online revocation check, which can be turned off), and links to other documents, files and web addresses with a permission per action.
Minimal
Without 3D
Full without the 3D code and without network code. It keeps the annotation tools, forms with field scripts, Protected Mode and signature checking; U3D and PRC models are not drawn, and revocation is read only from the proof inside the document.
Safe
Without active content
Minimal without forms, JavaScript, annotation tools, links that leave the document and the list of opened documents; that code is not compiled in. Annotations already in the file stay visible but are not interpreted. Meant for documents you do not trust.
| Module | Full | Minimal | Safe |
|---|---|---|---|
| Reading, printing, 6 formats | Yes | Yes | Yes |
| Text search and selection | Yes | Yes | Yes |
| Annotation tools (markup, notes, drawing) | Yes | Yes | Excluded |
| Annotations already in the file | Read and editable | Read and editable | Visible, never parsed |
| Opening password-protected PDFs (print, copy and edit restrictions not enforced) | Yes | Yes | Yes |
| Protected Mode | Yes | Yes | Excluded |
| Links within the document | Yes | Yes | Yes |
| 3D models (U3D, PRC) | Yes | Excluded | Excluded |
| AcroForm fields | Yes | Yes | Excluded |
| JavaScript in forms | Optional, on by default | Optional, on by default | Excluded |
| Links out of the document | Per-action permission | Per-action permission | Excluded |
| Online revocation check for signatures | On by default, can be turned off | Excluded | Excluded |
| Hardening | Always on | Always on | Always on |
The three install side by side, each with its own settings. For
example, Minimal can be the everyday reader and Safe the one you pick
in the right-click menu for an attachment you didn't expect. On Linux they are three packages
(montecristo, montecristo-minimal,
montecristo-safe); on Windows, one installer that lets
you pick any of them, or three portable folders.
Linux
.deb package
For Ubuntu and Debian-based distros. Install with a double-click or apt.
-
FullDownload Full .deb
Checksums
- SHA256
- 77a0059b5e38fc196a1e8b976c77621a510d34c1cb01826e114eab1be2c3cf19
- MD5
- 5259f859b1b5a2b7028a0a728dd8983d
-
MinimalDownload Minimal .deb
Checksums
- SHA256
- a417afafe10a607e5fc151e05eca961bdfa4f78efd4c4248acbbaf535c9c700b
- MD5
- e22f7d8583f09df246435f739b3ef13e
-
SafeDownload Safe .deb
Checksums
- SHA256
- 011af4ac4275ea9f9a0f852cd99eca06b4cfe7a36cc6ced01f611f95306776a8
- MD5
- e635a1ec848a26e067ab00fd523c5a70
Windows
Installer
Windows 10 and 11, 64-bit. One setup for all three variants: tick Full, Minimal, Safe or any mix (Full alone by default). It installs for your user only, no administrator rights, adds Start menu entries and offers each variant in “Open with” and in Settings › Default apps, where you choose your default PDF reader. Uninstall from Installed apps; run the setup again to add or remove variants.
-
Full · Minimal · SafeDownload installer .exe
Checksums
- SHA256
- 613f5d06c425a3c448eb6af0b83cb84b75dd2ea517f86b81a135f13d7c41f784
- MD5
- 0db5077a78dd26499e0434b374367dd4
The installer is not signed yet, so Windows may show “Windows protected your PC”: click More info, then Run anyway. Why?
Windows
Portable build
Windows 10 and 11, 64-bit. Nothing to install: extract the folder anywhere and run montecristo.exe (montecristo-minimal.exe, montecristo-safe.exe) — no separate dependencies.
-
FullDownload Full .zip
Checksums
- SHA256
- 0bdee46a572ad4fd4f98fbb460acacb3a8694eef0271f09ccc07cadda9615c84
- MD5
- df204b110e7b4cd7802cbe172b6498d1
-
MinimalDownload Minimal .zip
Checksums
- SHA256
- 43a4e036b84630013554b3148f661867e73ca5c6bdf2e37fddb59f95d1637799
- MD5
- dfcd1c5f928f52849b329f7862b31112
-
SafeDownload Safe .zip
Checksums
- SHA256
- 60c35c6055b779b9f6ca791bec477b4ca253c5bfd4fdc8d6d107281ce62d0d9d
- MD5
- 6ddf3896b53adff237efea12a03bee58
Every checksum above is also published as a file, so you can verify a
download without copying hex by hand:
SHA256SUMS ·
MD5SUMS.
Put the file next to what you downloaded and run
sha256sum --check --ignore-missing SHA256SUMS
(on Windows, Get-FileHash in PowerShell prints the SHA256).
Questions, answered.
Does Montecristo connect to the internet?
It depends on the variant and the version.
- Full: only to check whether a signer's certificate has been revoked, when a signed PDF doesn't carry that proof itself. The request goes to the authority that issued the certificate, which sees your IP address and which certificate is checked; only addresses on the public internet are contacted, never your local network. It is on by default. In Settings › Security, Check signatures online turns it off completely; turning off Check online automatically keeps it but sends a request only when you click Check online in the Protect bar.
- Minimal and Safe: never. They contain no network code at all.
In every variant there is no telemetry, no automatic update check and no account, and documents, settings and recent files stay on your computer. A web link in a document opens in your system browser, after you confirm the address; Settings has a switch for each kind of link. Trust in a signer never comes from the network: only from the certificates in your folder and the EU lists built into the program.
Which 3D models can it show?
U3D and PRC models embedded in PDFs, the two formats used by technical datasheets and CAD exports, in the Full variant. U3D and PRC files are each decoded in a separate process (time limit 5 seconds for U3D, 15 seconds for PRC), so a damaged model cannot crash the reader. Not drawn yet: PRC models stored only as exact B-rep bodies, 3D lines and PMI annotations. U3D animations and 3D JavaScript are not supported.
What is the difference between Full, Minimal and Safe?
Full has every module: 3D models, forms with field scripts, annotation tools, links with a permission per action and the online revocation check for signatures. Minimal is Full without the 3D code and without network code. Safe is Minimal without forms, JavaScript, annotation tools, links that leave the document and the list of opened documents; annotations already in the file stay visible but are not interpreted. In Minimal and Safe the excluded code is not compiled in, not just hidden from the menus. All three install side by side, each with its own settings.
Is there a Windows version?
Yes, for Windows 10 and 11, 64-bit, in two forms. The installer lets you pick Full, Minimal, Safe or any combination, installs for your user without administrator rights, and adds Start menu entries and an Installed apps entry to uninstall. The portable zip needs no installation: extract the folder anywhere and run montecristo.exe (montecristo-minimal.exe or montecristo-safe.exe for the other variants). Neither needs separate dependencies. There is no macOS version.
Can Montecristo be my default PDF reader on Windows?
Yes. The installer registers each variant it installs as a program that can open PDFs and, from 0.3.9, EPUB, XPS, CBZ and FB2 files, each with its own file icon, so it shows up in “Open with” and in Settings › Apps › Default apps. Windows doesn't let a program make itself the default: you pick it there, once.
Windows says “Windows protected your PC”. Is that a problem?
No. The installer isn't signed with a code-signing certificate yet, and SmartScreen warns about any unsigned program it hasn't seen many times. Click More info, then Run anyway. If you want to be sure the file is the one we published, compare its SHA256 with the checksum on this page before running it.
Which certificates does signature checking trust?
The ones you put in the trusted certificates folder (Protect bar → Open the trusted certificates folder), and the qualified certificate authorities of the EU national trusted lists, which are built into the program. Not your browser's or operating system's, not the Mozilla bundle (those certificates are approved for websites, not for signing documents), and not Adobe's list. The built-in lists were verified, when this version was built, against the six certificates the European Commission uses to sign the EU List of Trusted Lists, as published in the Official Journal of the EU (C/2026/1944):
- Patrick Kremer (Signature) · expires 30 May 2028
D2:06:4F:DD:70:F6:98:2D:CC:51:6B:86:D9:D5:C5:6A:EA:93:94:17:C6:24:B2:E4:78:C0:B2:9D:E5:4F:84:74 - IOANNA KALOGEROPOULOU · expires 23 November 2029
C0:64:1C:4F:7D:56:C4:31:B1:C9:24:74:2D:B7:FC:E9:C1:EE:F7:D7:FD:21:21:13:A2:76:84:86:B3:AB:CD:C5 - VICENTE ANDREU NAVARRO · expires 6 May 2027
DF:7E:29:36:0C:34:B2:B8:D6:D5:F4:03:25:C1:D4:D1:2C:99:22:CE:CD:33:B7:40:76:74:A7:4B:2B:3C:A1:E5 - APOSTOLOS APLADAS · expires 26 April 2027
B6:3D:41:67:44:E7:09:8B:F9:EC:2C:AA:59:6A:93:BC:24:68:E3:7F:82:84:BA:65:EC:C0:61:71:1B:CB:AA:18 - EUROPEAN COMMISSION · expires 17 November 2027
E0:A6:20:FB:B6:74:73:62:BB:93:3A:C4:41:69:D6:76:A5:53:44:47:16:CF:5F:31:60:5F:12:A2:2B:83:96:B1 - EUROPEAN COMMISSION · expires 17 December 2029
23:61:03:F0:3A:80:31:AE:8F:47:F9:05:9B:F8:DE:38:56:4C:DB:FE:BE:DD:E4:A5:97:D5:0F:89:80:AA:65:3B
Names are the certificates' common names; the codes are their SHA-256 fingerprints. The built-in lists hold 872 qualified certificate authorities and 1,078 timestamping authorities from 30 of the 31 national lists (Latvia's could not be downloaded). Timestamping authorities are kept in a separate list and count for timestamps only. The app makes no network request to refresh them: the date of the lists is shown in the signature panel, and after six months the panel suggests installing a newer version. Outside the EU nothing changes: trust comes only from the certificates in your folder.
Which formats besides PDF?
EPUB, XPS and OpenXPS, CBZ, FictionBook and SVG, in the same interface. Annotations, forms and passwords apply to PDFs only. EPUB, XPS, FictionBook and SVG can be searched and their text selected; CBZ comics are shown without search or text selection. DjVu, MOBI, CBR and plain image files are not supported.
What happens if a PDF uses a font Montecristo doesn't have?
Nearly every PDF embeds its fonts, and those are drawn as stored. When a font is only named, not embedded, Montecristo swaps in the closest built-in font and stretches each letter to the original width, so the text stays readable and the layout doesn't move; only the look of the letters changes. Chinese, Japanese and Korean get the built-in CJK font. A character that is missing from the substitute font shows as an empty box or a blank. Montecristo never downloads fonts.
Are my annotations readable in other programs?
Yes. Every mark is saved as a standard PDF annotation. Save appends the changes to the end of the same file, leaving the original content untouched. If that isn't possible (for example, a PDF with a damaged structure), Montecristo by default replaces the file with a complete rewritten copy; you can turn that off in Settings. Save As and password-protected copies are written to a new file. Montecristo adds annotations and text watermarks; it does not edit the existing text or images of a page, merge or reorder pages, run OCR or create forms.