Montecristo

PDF reader · Linux & Windows

PDF, finally in three dimensions.

Montecristo opens your documents instantly, lets you annotate, fill in and protect them — and when there's a 3D model inside, it spins right in front of you. Native, light, no telemetry.

U3D and PRC 3D models embedded in PDFs — finally on Linux too

Download free See what it can do
6
formats: PDF, EPUB, XPS, CBZ, FB2, SVG
14
standard annotation types
0
telemetry, accounts, ads
2
platforms, one native app on both

Why Montecristo

Five things that make the difference between a viewer and a working tool.

3D inside PDFs The headline feature

That 3D model was always there. Now you can see it.

Technical datasheets, CAD drawings, scientific papers: many PDFs contain 3D models that most readers show as an empty rectangle. Montecristo decodes them — both U3D and PRC — and puts them in your hands.

  • Rotate, pan, zoom with the mouse, smoothly.
  • Preset views X, Y, Z and isometric, with 60 fps animated transitions.
  • Four render modes: solid, wireframe, vertices, transparent.
  • Original colors, materials and textures from the model.
  • Broken-file safe: 3D runs in an isolated process; a corrupted model can't take the reader down with it.
Annotations

Write on the PDF like paper. Readable everywhere.

Highlight, underline, strike through, comment, draw. Every mark is saved as a standard PDF annotation: whoever receives the file sees it in Acrobat, Foxit, or any other reader.

  • Highlight, underline, strikeout and squiggly, anchored to the text.
  • Pen, sticky notes, free text, rectangles, ellipses, arrows, polygons.
  • Move, resize, rotate, copy and paste what you've drawn.
  • Quick palette and a free color picker.
  • Non-destructive saving: the original file is never rewritten in place.
Forms

Forms you can fill in. That do the math themselves.

Text fields, checkboxes, radio buttons, dropdowns, list boxes: all fillable right on the page. If the form has calculations or validation logic, Montecristo runs it.

  • Form JavaScript: totals, validation and calculated formats, run automatically.
  • Tab and Shift+Tab navigation, keyboard activation.
  • Required fields flagged, read-only fields respected.
Security

A PDF doesn't get to decide for you.

A document can contain links to other files, scripts and commands. Montecristo treats them for what they are: untrusted content. You decide what's allowed to happen.

  • No program is ever launched from a link in the document.
  • Separate permissions for internal jumps, other documents, the web, and new windows.
  • Form JavaScript can be switched off with one click.
  • Password-protect a PDF, with strength measured in bits as you type it.
  • Zero outbound connections: there is no networking code in the app at all.
  • Digital signatures for documents: coming soon.
Performance

A thousand pages, zero waiting.

Montecristo only renders what you're actually looking at, and prepares the next pages ahead of time. Scrolling stays smooth even on the heaviest documents, and the interface never freezes while it works.

  • Rendering on a separate thread, the next 6 pages pre-loaded.
  • Memory freed for pages that scroll out of view.
  • Performance panel: memory and cached pages, per tab.
  • MuPDF engine: compact, fast, battle-tested for years.

The philosophy

Three principles, in this order. If a new feature breaks one of them, it doesn't ship.

01

Actually light

Opens instantly and stays nimble even with documents thousands of pages long. No browser wearing an app costume: underneath is MuPDF, a rendering engine built to do exactly this, and do it well.

02

Native, not a compromise

A real GTK4 interface on Linux, the same care on Windows, with a native title bar and system snap. No Electron, no wrapper: it behaves the way your operating system taught you to expect.

03

Respects the reader

Zero telemetry, zero accounts, zero ads, zero connections. What you read stays on your computer. Full stop.

And then, everything else you'd expect

The basics of a good reader, built with the same care.

Multiple tabs

Many documents, one window. Drag files in: each opens its own tab, and a file that's already open won't be duplicated.

Not just PDF

Also reads EPUB, XPS and OpenXPS, CBZ comics, FictionBook and SVG, in the same interface.

Search and selection

Ctrl+F finds it instantly. Select text with the mouse and copy it wherever you need.

Outline and links

Clickable side outline, internal and external links, jumps between linked documents.

Images, one click away

Right-click an image on the page: copy it, save it, or read its EXIF data.

Watermark

Add a text watermark with the size, color, opacity and rotation of your choice.

Source view

For those who want to look under the hood: the PDF as indented text, editable object by object.

Zoom and rotation

Fit width or page, Ctrl+wheel zoom, instant rotation, middle-button pan.

Digital signatures Coming soon

Verify signatures on documents you receive, and sign your own PDFs with a certificate. Among the next things on the list.

English and Italian

Translated interface, with more languages on the way.

Download

Three builds of the same reader. They differ only in which modules are compiled in — pick how much of a PDF you want this program able to touch.

All three are hardened builds. Symbols stripped, no debug logging compiled in, hidden symbol visibility, aggressive inlining. Hardening is not something you choose here: nothing is published without it.

Full

Everything

The whole reader. 3D models (U3D and PRC) rendered in an isolated process, AcroForm fields with their JavaScript, and links that can leave the document — each behind its own permission under Settings > Security.

Minimal

No 3D

Full, minus the 3D modules: the U3D decoder, the PRC parser and the GL renderer are not compiled, and the vendored 3D library isn't shipped. A /3D annotation falls back to the placeholder box MuPDF draws itself. The package is about 6 MB smaller.

Safe

Smallest attack surface

For PDFs you don't trust. Minimal, minus everything a document can use to make the program act: no AcroForm fields, no JavaScript at all — the interpreter isn't even compiled into MuPDF — no annotation tools, and no link that leaves the open document, not even behind a confirmation dialog. There is no dialog, because there is no code behind it. Annotations already in the file stay visible — MuPDF draws them as part of the page — you just can't touch them, and this build never parses them.

What each build contains
Module Full Minimal Safe
Reading, printing, 6 formats YesYesYes
Text search and selection YesYesYes
Annotation tools (markup, notes, drawing) YesYesNot compiled
Annotations already in the file Read and editable Read and editable Visible, never parsed
Passwords and permissions YesYesYes
Protected Mode YesYesYes
Links within the document YesYesYes
3D models (U3D, PRC) YesNot compiledNot compiled
AcroForm fields YesYesNot compiled
JavaScript in forms Optional, on by default Optional, on by default Engine not compiled
Links out of the document Per-action permission Per-action permission Not compiled
Hardening Always onAlways onAlways on

The three install side by side and share nothing — not a file, not a setting. That's deliberate: keep Minimal as your everyday reader and open the attachment you weren't expecting with Safe, from the same right-click menu. On Linux they are three packages (montecristo, montecristo-minimal, montecristo-safe); on Windows, three folders.

Linux

.deb package

For Ubuntu and Debian-based distros. Install with a double-click or apt.

Download .deb v0.2.0 · hardened
SHA256
f37ee9658ce9b1269490ea921b9eba1c2a761cef5fc948c2ac4e8f3f3c1530b1
MD5
a2b6d2a2379c1a067a4b6b17a19aa7e9
Linux

Portable build

Self-contained archive, no installation: extract and run.

Download .tar.gz v0.2.0 · hardened
SHA256
041045dd0d14af7af16285edb71af7264d21cad1aa87e15c15fd0e37decde41c
MD5
9abe0f0e7244a3a8f818fea7c073f863
Windows

Portable build

Windows 10 and 11, 64-bit. Extract the folder and run pdfviewer.exe — no separate dependencies.

Download .zip Not published yet

No Windows package has been published yet, for any build. The script exists but needs an MSYS2/UCRT64 machine to run: .\scripts\package_windows.ps1 -Variant full

Linux

.deb package

For Ubuntu and Debian-based distros. Install with a double-click or apt.

Download .deb v0.2.0 · hardened
SHA256
c3cc26e3f5dacafeaed034ed4f07f7bca92a4315744126400d3e7eba58787065
MD5
8b3f8af274de332ad423a65cd6acde06
Linux

Portable build

Self-contained archive, no installation: extract and run.

Download .tar.gz v0.2.0 · hardened
SHA256
5975dd3541a227de1aac7e17348b2ea9c926bfce64bf6ed806045328ba9f038c
MD5
48e4b6e7b18e4cd3a50bd44a61cbc463
Windows

Portable build

Windows 10 and 11, 64-bit. Extract the folder and run pdfviewer.exe — no separate dependencies.

Download .zip Not published yet

No Windows package has been published yet, for any build. The script exists but needs an MSYS2/UCRT64 machine to run: .\scripts\package_windows.ps1 -Variant minimal

Linux

.deb package

For Ubuntu and Debian-based distros. Install with a double-click or apt.

Download .deb v0.2.0 · hardened
SHA256
5d3524366878d03b934a2ddd79059bb6f7811a57150fd75f44e0a64fb6530682
MD5
90da3b89331c03bc8abc8080abd1ada9
Linux

Portable build

Self-contained archive, no installation: extract and run.

Download .tar.gz v0.2.0 · hardened
SHA256
ab2db09ce266276081f242ae660d5c36d037def883c87d2b84cd118dcb88fc76
MD5
0fa4a4b56a1b56dac868992582a63271
Windows

Portable build

Windows 10 and 11, 64-bit. Extract the folder and run pdfviewer.exe — no separate dependencies.

Download .zip Not published yet

No Windows package has been published yet, for any build. The script exists but needs an MSYS2/UCRT64 machine to run: .\scripts\package_windows.ps1 -Variant safe

Changelog

History of published versions. Full detail in the repository.

Version Date Highlights
0.2.0 2026-10-02 Three builds instead of one — Full, Minimal, Safe — which differ only in which modules are compiled in, and install side by side without sharing a file or a setting. All three are hardened; the earlier claim that published packages were built without hardening was simply wrong. The Safe build drops the 3D modules, AcroForm fields, the JavaScript engine (MuJS isn't compiled at all), the annotation tools, and every link action that leaves the document.
0.1.19 2026-09-30 Rebrand to Montecristo (app ID, icons, .desktop entry). Fixed a packaging bug where the runtime anti-debug check (ptrace-based, Linux only) exited immediately on systems where ptrace is restricted for reasons unrelated to an actual debugger — the app simply wouldn't start after install, with no visible error. That check has been disabled on Linux; the rest of the hardening build is unaffected.
0.1.18 2026-09-28 First packaged build (.deb/.tar.gz) and site published. Italian/English localization. Fixed 3D model (U3D) colors and transparency. Fixed a page not rendering after a scrollbar drag; reopening an already-open file now focuses the existing tab instead of duplicating it. Password strength shown in bits, saving with imported annotations, viewer notes saved as standard PDF comments.
0.1.14 — "Fit width" zoom centers the page horizontally. Hand-drawn icons wired into the build.
0.1.13 — First version with an explicit SemVer number.
earlier — 157 commits with no explicit versioning: a GTK4 + native MuPDF viewer for Linux built from scratch — text search/selection, clickable links, U3D/PRC 3D annotations, password-protected PDFs, settings, document properties.