Why edited PDFs usually look edited

Most tools drop a text box over the old words. You end up with a different typeface sitting slightly off the baseline. Quokka changes the file itself.

It edits the real file

Your text goes into the document's own content stream, on the same baseline, in the same font. There's no white patch with fresh type over it. Images, drawings and the other pages don't change at all.

No hollow boxes

A PDF normally carries a cut-down font holding only the characters already on the page. Ask for one that isn't in there and most editors draw an empty square. Quokka borrows a matching face, and says which characters it had to borrow.

Nothing is uploaded

The PDF engine is WebAssembly and it runs in this tab. No upload, no copy on a server, no server at all. Unplug your network and it keeps working.

Same edit, two tools

Retyping a heading on a bank statement. The bold font inside it carries 45 characters and not a single digit.

A typical online editor

Quokka

Invoice . The digits aren't in the font, so they come out hollow.

Invoice 158. The three missing digits come from a matching face, and you're told which ones.

Your file is uploaded to be processed.

Your file stays in the tab.

The edited line lands in a slightly different typeface.

The edited line keeps the document's own font and spacing.

How it works

MuPDF, compiled to WebAssembly, renders the page in a background thread. Every line of text gets an invisible hit area over it, so a click picks the run you can see. Retype it and the old glyphs come out of the content stream; the new ones go in where they were.

Matching the type

Embedded fonts are nearly always subsets. They hold the characters the document used and nothing more, and plenty of them ship without a usable character map. Ask one to spell a new word and you get boxes.

So every character is written with the font's own code, dug out of the file. Widths come from measuring where the real glyphs sit, because a subset's own metrics are often nonsense. There's one more wrinkle: a single line frequently uses more than one font. Browsers split them, so a date like 21 Sep 2026 can draw its letters from one font and its digits from another. Each character goes to whichever font on that line can actually draw it.

Limits

Text doesn't reflow. Type something longer and it runs into whatever sits to its right, the same as in every other PDF editor. Scanned pages have no text to click, so they need OCR first; you'll get a note when one turns up. Editing a signed PDF breaks its signature, and you'll be warned before you start.

Edit a PDF like it's a piece of paper