A PDF is hard to edit because it stores a finished layout, with text at fixed coordinates that does not reflow. Small fixes work in place. Rewrites belong in another format.
How a PDF stores text
A Word document stores paragraphs, headings and styles and computes the layout when opened, so text reflows. A PDF stores the finished layout: glyphs at exact coordinates, plus lines and images. One paragraph can be dozens of separate text fragments, often with no space characters between words, only gaps. This keeps the layout identical on every device and printer, and makes editing hard.
Font subsetting
PDFs usually embed font subsets containing only the characters used. If the document has no "Z", the font may lack one, and new text needs a substitute font with different shapes or spacing.
PDF text does not reflow
Replacing "cat" with "elephant" in a PDF moves nothing else, so the new word overlaps its neighbors or leaves a gap. In-place editing suits local fixes such as a name, date, figure or logo.
Scanned PDFs
PDFs from a scanner or phone camera contain only page images, no text. OCR (optical character recognition) must extract the text first, and its output always has errors. Use the original digital document when you can get it.
Ways to edit a PDF
- Small corrections: the PDF text and image editor rewrites, deletes and adds text and replaces images. Unusual fonts may need substitution.
- Comments and review: the PDF annotator adds highlights, underlines and notes.
- Page-level changes: the page editor and merge tool remove, reorder and combine pages without touching text.
- Heavy rewriting: extract the text with the PDF-to-Markdown or PDF-to-text converter, edit it elsewhere, and build a new document. The original layout is lost.