One executable and PDFium. No installer, no runtime, no framework — extract the folder and run it.
It reads, searches and marks up PDFs without leaving marks on the page: the text you select stays selectable, every highlight and pin is undoable on its own, and the file you opened is never rewritten unless you ask.
A reader should stay out of the way of the document. mnpdf scrolls pages continuously in a single column, and the marks you make are drawn over the text rather than replacing it, so a highlighted sentence is still a sentence you can select, copy and search for.
Annotation is meant to feel like a marker on paper. Right-click highlights the selection or drops a pin with a note, and both live in the same palette: six presets, plus up to three custom #rrggbb colours you type yourself. An entry that is not a colour is explained straight away instead of being silently ignored.
Nothing you do to a page is a one-way door. Each highlight and pin is undoable and redoable individually, and deleting a mark is itself an undoable operation rather than a loss of information. With autosave on, the marks wait in a sidecar file while the PDF on disk stays exactly as you opened it.
Pen: Amber. Pick a phrase, then mark or clear it.
A sketch of the real highlighter, on a passage written for this page. The app's own marks are made with a right-click and undone with Ctrl+Z.
Pages scroll continuously in a single column. Zoom with the mouse wheel while holding Ctrl, or with + and -, and fit the page width with Ctrl+0. The scroll bars move in both directions.
Select with the mouse and copy with Ctrl+C. Ctrl+F searches, F3 and Shift+F3 step forward and back through matches, and Esc closes the search bar.
Right-click highlights selected text, or adds a pin with a note. Highlights and pins share one palette of six presets plus up to three custom colours you enter yourself; Clear custom colours hands the slots back.
Everything is individually undoable with Ctrl+Z and redoable with Ctrl+Y. A pin's note stays with the pin through undo, so stepping back does not strand the annotation.
Rotate the current page either way from the right-click menu; the rotation persists with the document. Insert a signature by handing it a JPEG and clicking the page where the stamp should land — a file that is not a JPEG is refused rather than decoded.
Merge PDFs appends other files to the document you are reading. Split pages exports a range such as 2-5 or 1,3,8 into a new PDF, leaving the original untouched.
Everything the app remembers sits under %APPDATA%\mnpdf. app.txt holds the settings — titlebar, tab strip, autosave, default colours, night mode, window geometry. doc-<hash>.txt holds one document's zoom, page, highlights, rotations, pins and signatures.
With autosave on, which is the default, edits are written to that sidecar and the PDF on disk is left untouched. Ctrl+S is the point where the marks move into the file: the document is written and reloaded from what was saved, so the annotations stop being a separate bookkeeping file and become part of the PDF.
One window holds several documents. Ctrl+T opens a tab, Ctrl+W closes it, Ctrl+Tab cycles, and the strip along the top switches by click. Each tab carries its own document, page, zoom, marks and undo history, so leaving and coming back leaves everything where it was. A dot in front of the name means that tab has unsaved changes.
Hide tab strip takes the strip away for a taller view and the choice is remembered; the keyboard still moves between tabs while it is hidden. Running mnpdf.exe twice gives two independent windows, so two PDFs can sit side by side. The first window owns the remembered settings and what a plain launch reopens; later windows read those settings but start empty.
The app checks for a newer release at most once an hour and tells you when one exists. The check button then becomes an update button: it downloads the official ZIP, replaces the executable and DLL in the folder the app runs from, and restarts. An unsaved document blocks the swap until you save it, and a failed download changes nothing on disk.
That check is the only outbound request the reader makes. There is no account, no telemetry and no cloud sync, but it would be wrong to say the program never touches the network, so this page does not.
The portable ZIP carries four files: mnpdf.exe, pdfium.dll, README.txt and PDFIUM-LICENSE.txt. Keep the DLL next to the executable — the two are a matched pair. Nothing is registered, and the folder can be copied to another machine or a USB stick as-is.
PDFium is used under the BSD-3-Clause license, and its license text ships inside every release ZIP. The latest release tag at the time this page was written was v2.5.0; the link below always points at whatever is newest.
No installer to run. Quit, delete the folder, and it is gone.