Edit a PDF: add text and shapes to its pages
Editing a PDF here means adding new content — text boxes and simple shapes — on top of the existing pages, which stay untouched underneath. The tool runs entirely in your browser, so the document is never uploaded. It cannot reflow, restyle, or delete text that is already in the file; for filling in blanks, labeling drawings, or completing scanned forms, an overlay edit is exactly what is needed.
How it works
Every PDF page has a content stream: an ordered list of drawing operators that a viewer executes top to bottom — set this font, move here, show this string, fill this rectangle. A page's final appearance is simply the result of running the whole list. That design makes appending easy and rewriting hard. Adding a text box means appending a handful of operators to the end of the stream, where they paint after (and therefore on top of) everything already there. Changing an existing word, by contrast, would require locating its operators mid-stream, editing them, and re-laying-out everything the change displaces — which is why this tool adds but does not alter.
To let you position additions accurately, the tool first renders each page to the screen with the pdf.js engine. Your clicks are recorded in screen pixels, then converted to PDF user-space coordinates, whose origin is the bottom-left corner of the page and whose unit is the point (1/72 inch). When you save, pdf-lib writes the new operators into each edited page's content and serializes the whole document again.
Added text uses the standard 14 fonts — Helvetica, Times, Courier, and their bold/italic variants — which every PDF viewer must supply, so no font file needs embedding and the file grows only by a few hundred bytes per edit. The document's own fonts cannot be reused for new text because they are almost always subsets: an embedded font containing only the 40 glyphs the document happened to use has no letters left for yours.
One honest caveat: an overlay is paint, not erasure. A white box drawn over a paragraph hides it on screen and in print, but the paragraph's operators are still in the file and its text can still be extracted. When content must actually be removed, use the redaction tool, which flattens pages so the underlying text is gone.
Worked example: completing a scanned application form
You receive application.pdf — a 2-page scanned form, 1.6 MB, with no interactive fields because it is just a picture of paper. Printing, handwriting, and re-scanning is the workflow to avoid.
Load it in the editor instead. On page 1, click the "Name" line and type your name in 11 pt Helvetica; repeat for the address and date lines — six text boxes in all. On page 2, draw a small filled rectangle over the pre-printed checkbox for "Option B" to mark it. Saving takes under a second, and the output is 1.61 MB: the scan's two images pass through untouched, and the six text boxes plus one rectangle add roughly 3 KB of new operators and structure. The typed entries are crisp vector text, so they stay sharp when the recipient zooms in, and they are selectable and searchable even though the form underneath is a scan.
Edit PDF — frequently asked questions
Can I delete or change the existing text in my PDF with this tool?
No. This editor overlays new text and shapes on top of the page; the original content is untouched underneath. You can visually cover old text with a filled box and type over it, but true text replacement needs a desktop editor with the original fonts.
Why does my added text look different from the fonts in the document?
New text is set in one of the 14 standard PDF fonts, such as Helvetica or Times, which need no font file to be embedded. The document's own fonts are usually subsets missing many letters, so they cannot safely be reused for new text.
Will the text I add to the PDF be selectable and searchable?
Yes. Added text is written as real PDF text operators, not as an image, so any viewer can select, search, and copy it. This also keeps the file small — a few hundred bytes per text box.
Is my document uploaded anywhere while I edit it?
No. The pages are displayed and the edits are written into the file by JavaScript running in your browser tab. The document stays on your device from start to finish.
Can the additions be removed by someone after I save the edited PDF?
The additions become ordinary page content, which a determined user with PDF software could edit again, and anything you covered with a box still exists underneath. For genuinely removing sensitive content, use a redaction tool that flattens pages instead.
Can I edit a scanned PDF and add text to it?
Yes, because overlaying does not care what the page contains — a scanned image accepts new text boxes just like a digital page. Filling in a scanned paper form is exactly this use case.