What the PDF viewer does
The viewer opens a PDF from your device and renders every page in the browser as a scrollable sequence of images, using PDF.js — the same engine Firefox uses. It exists for the situations where the usual options fail: a locked-down computer with no PDF software, a browser configured to download PDFs instead of showing them, a file that another viewer refuses to open, or simply wanting to check a document without saving it anywhere. Nothing is uploaded; the file is read into memory and drawn on your screen.
How it renders
Each page is rasterized at 1.5× its nominal size — about 108 dpi — which is sharp on a laptop screen and readable on a phone when zoomed. Rendering is sequential, so the first page appears almost instantly and the rest follow; a 100-page document takes a few seconds. Because the output is a set of images, you scroll through it like a long web page and can zoom with the browser's normal controls. Text is not selectable in this view; if you need to copy text, use PDF to TXT.
When to use it
- Previewing before processing — check page order, blank pages or orientation before merging, splitting or deleting.
- Files that will not open elsewhere — PDF.js is tolerant of slightly malformed files that stricter viewers reject.
- Shared or restricted computers — kiosks, library machines and locked-down work laptops without a PDF application.
- Suspicious attachments — viewing as images means no embedded JavaScript, forms or links are executed or followed.
- Quick reads on a phone — no app install, no upload to a cloud viewer.
What it does not do
| Feature | Available? | Alternative |
|---|---|---|
| Text selection and search | No | PDF to TXT to extract text |
| Filling forms | No | Acrobat Reader, browser's built-in viewer |
| Following links and bookmarks | No | Browser's built-in viewer |
| Annotating and signing | No | Desktop editor or your OS's markup tools |
| Password-protected files | No | Unlock PDF first (you need the password) |
| Printing | Via browser print of the page | Open in a native viewer for proper page-by-page printing |
Tips
- Use the browser zoom (Ctrl/Cmd + and −) to enlarge small text; the images are rendered with enough resolution for about 2× zoom.
- Very large documents (500+ pages) use memory proportional to the page count; on phones, extract the pages you need first.
- Pages are shown in file order at their stored rotation, so a sideways scan will appear sideways — a good way to spot pages that need Rotate PDF.
- Reload the page to close the file; nothing persists once you leave.
Privacy
The PDF is read with the browser's FileReader API and rendered on canvas elements. No part of it is transmitted. This makes the viewer suitable for documents you would not put into a cloud preview — contracts, medical records, unpublished manuscripts. You can confirm by loading the page, disconnecting from the network, and opening a file.