How to edit a PDF in Firefox

What Firefox's built-in PDF viewer can and can't do

When you open a PDF in Firefox, you get the pdf.js viewer with a small toolbar across the top. It's genuinely useful for lightweight markup, and everything stays on your device.

The catch is that it only adds a layer on top of the page. It treats your document as a fixed image you can write on, not as text you can rewrite.

• You can: add a text box, draw freehand, highlight passages, and insert an image or signature on top of the page.
• You can't: change words that are already printed in the PDF, match the document's original font when adding text, or rotate, delete, and reorder pages.
• Saved annotations are a stack of overlays, so they may not always line up with the look of the underlying text.

When the built-in viewer is enough

If your task is fast and informal, Firefox's own annotator does the job without any extra tools.

Reach for it when you just need to scribble a note in the margin, highlight a clause for a colleague, or drop a quick text comment before sending the file back. There's nothing to install and nothing leaves your computer.

When you need a real PDF editor in Firefox

The moment you need to change what the document actually says (fix a typo in a contract, update a date, or correct a number on an invoice) the built-in viewer falls short. It can't touch the existing text, so people often resort to slapping a white box over the old words and typing on top, which looks obviously patched.

A local browser editor solves this. It loads in the same Firefox tab, reads the font embedded in your PDF, and rewrites the text using that exact font, size, and color. The edit blends in instead of looking pasted on.

• Edit existing text in place, matching the document's real embedded font.
• Add new text that auto-matches the size and color of nearby text.
• Sign by drawing or typing a signature, and add stamps like Approved or Paid.
• Insert logos and images, highlight, draw shapes, and add sticky notes.
• Rotate, delete, and reorder pages, then download the finished file.

How to edit a PDF in Firefox, step by step

Because the editor renders your file with pdf.js right in the browser, the same approach Firefox's own viewer uses, your PDF is never uploaded to a server. Everything happens locally on your machine, which matters for contracts, statements, and anything with personal details.

• Open the local browser-based editor in Firefox (no install, no signup).
• Drag your PDF onto the page, or click to choose a file from your computer.
• To change wording, click the existing text and type over it; the editor keeps the original font.
• Add a signature, stamp, image, highlight, or note as needed using the toolbar.
• Manage pages if required, then click Download to save the edited PDF back to your device.

A quick note on privacy

One reason to keep PDF editing inside Firefox is that the file stays put. Many web tools upload your document to process it; a local editor reads it into the browser's memory and writes the changes back without a network round trip.

You can confirm this yourself: open Firefox's developer tools, switch to the Network tab, and watch while you edit. With a truly local editor, no request carries your file. You can even disconnect from Wi-Fi after the page loads and keep working.