What editing a PDF can and cannot mean
People asking to edit a PDF usually want one of two very different things. The common one is adding something: a date in a blank, a tick in a box, a signature, a stamp, a correction blanked out and rewritten. The rarer one is rewriting the existing text so the paragraph reflows, the way you would in a word processor. This tool does the first properly and does not pretend to do the second.
The reason is in the format. A PDF stores instructions to draw glyphs at fixed coordinates. There are no paragraphs, no line breaks and no styles — that structure was used to produce the coordinates and then discarded. Changing one word means recalculating the position of every glyph after it, with only a subset of the font embedded. Editors that claim to do it are either reconstructing a guess at the layout, which is what makes PDF to Word disappointing, or quietly rasterising the page.
What you can add
| Element | Use it for | Note |
|---|---|---|
| Text | Dates, names, reference numbers, short corrections, APPROVED or DRAFT | Helvetica, in a colour you choose, at any size |
| Filled box | Blanking a line before writing over it, highlighting, separators | White to blank, black to cover, any colour to mark |
| Image | A signature, a company seal, a logo, a QR code | PNG keeps transparency; JPG does not |
Everything is drawn into the page with pdf-lib rather than rendered to a picture, so the document's original text stays selectable, the file stays small, and the pages you did not touch are byte for byte what they were.
Blanking out is not redaction
A white box over a line hides it on screen and leaves the text in the file, where a copy-paste or a text extractor finds it immediately. That is fine for tidying a form and completely unsuitable for removing anything confidential. If the point is that nobody should be able to read what was there, use Redact PDF, which re-renders the page and removes the text layer with it.
Which tool for which job
- Filling in a form with real fields — use Fill PDF Form. If the document has AcroForm fields, typing into them is cleaner than placing text on top, and the values can be flattened afterwards.
- Adding a signature — Sign PDF is purpose-built, with sizing and placement made for it.
- Stamping every page — PDF Watermark applies text across the whole document in one step; placing it page by page here would be tedious.
- Numbering pages — Add Page Numbers handles the counting, the corner and the starting number.
- Putting a letterhead behind a document — PDF Overlay stamps one PDF over another and keeps both sets of vectors.
- Rewriting a paragraph — go back to the source document and export a new PDF. It is faster than any workaround and the result is correct.
Placing things accurately
- The click marks the top left of what you place, not its centre. For text, that means the top of the letters.
- Zoom the page in your browser before placing something that needs to line up with a printed rule. The preview scales with the page.
- Place, check, then apply. Items show on the preview with a dashed outline so you can see the result before committing.
- Sizes are relative to the page, so a box set to 25% width is a quarter of the page on A4 and a quarter of the page on Letter.
- Non-Latin text — Helvetica covers Latin characters. Thai, Chinese, Japanese, Korean, Cyrillic and Arabic will not render correctly; place those as an image instead.