PDFs are harder to edit than word-processing files because they store a finished page layout rather than a flowing document structure. In practice, a PDF is closer to a set of drawing and printing instructions.
A PDF is a drawing, not a text file
A Word document stores structure: paragraphs, headings, styles; with layout computed fresh every time you open it, which is why text reflows when you edit. A PDF stores the result of layout: place these glyphs at these exact coordinates, draw this line here, put this image there. A paragraph, to a PDF, may be dozens of separately positioned fragments of text. There's no "paragraph" object to edit; often there isn't even a space character between words, just glyphs positioned far enough apart to look like a space.
This structure keeps the layout consistent across devices and printers. It also makes editing difficult.
The font problem
PDFs usually embed font subsets containing only the characters used in the document. If a page contains no letter "Z", the embedded font may not include it. New text can require a substitute font with different shapes or spacing.
No reflow means every edit is local surgery
Replace the word "cat" with "elephant" in a Word file and the whole paragraph reflows. In a PDF, nothing moves: the new word either overlaps its neighbors or leaves a gap, because every other fragment on the page has fixed coordinates. Realistic PDF editing is therefore local surgery; swap a name, fix a date, correct a figure, replace a logo; not rewriting paragraphs. For heavy rewriting, the PDF is the wrong place to work.
Scanned PDFs: the special case
If the PDF came from a scanner or a phone camera, there is no text in it at all; each page is a photograph. Nothing described above even applies until OCR (optical character recognition) has guessed at the text, and OCR output always contains errors. If you can possibly obtain the original digital document instead of a scan, do.
Realistic strategies, from light to heavy
- Small corrections: use the PDF text and image editor to rewrite or delete text, replace images, and add new text. Unusual embedded fonts may require substitution.
- Comments and review: use the PDF annotator for highlights, underlines, and notes.
- Page-level changes: removing, reordering or combining pages avoids the text problem entirely; that's the page editor and merge tool.
- Heavy rewriting: get the content out. The PDF-to-Markdown and PDF-to-text converters extract the text so you can rewrite it in a real editor and produce a fresh document; accepting that the original visual layout is left behind.
The general rule: the closer your task is to "change what this page says in one spot," the better in-place PDF editing works. The closer it is to "rewrite this document," the sooner you should leave the PDF format.