First, what a PDF is
A PDF stores drawing instructions: put this glyph here, this image there, in this font, at this size. It has no paragraphs, no flow, and often no complete font — just the characters the document used. That is why editing a PDF is nothing like editing a Word document, why “edit” tools behave so differently from one another, and why the honest first question is: which of the six jobs below do you actually have?
Job 1: fix a word, a date, a name
Changing existing text is possible when the font in the file has the glyphs you need. Open Edit and mark up, choose Replace text, click the run and retype it. Bindery decodes the text a run draws, re-encodes your replacement with the same font, and — when a subset font lacks a character — sets the run in a standard font and tells you, rather than turning the page into a picture. Expect this to work for numbers, dates and short phrases; a whole paragraph re-flowed to a new length is a Word job.
Job 2: add something to the page
Text labels, highlights, boxes and white-out go straight onto the page with Markup, drawn permanently into the content. A signature goes on with Sign — drawn or typed, placed with a live preview. A stamp on every page — DRAFT, CONFIDENTIAL, a client name — is Watermark. Page numbers and legal stamps are Page numbers and Bates numbering, written as real text.
Job 3: remove or move something
Edit objects shows every image and text block on the page as a selectable box. Delete removes it from the content stream; move and resize wrap it in a transform. The rest of the page is untouched and text stays text. Two honest limits: objects nested in form XObjects (common in office exports) are counted but not yet editable, and text is handled as blocks — for the words, see Job 1. To remove information rather than an object, the tool is Redact, which re-renders the marked pages without the text underneath; white-out only covers pixels.
Job 4: change the pages
Reordering, rotating and deleting pages is Organize, on a board of real thumbnails. Pulling pages out is Extract; cutting the file into parts is Split; combining files is Merge, or Mix pages when the pages must interleave. Page size is Resize, the visible area is Crop. All of these copy page content unchanged.
Job 5: fill it in
If the PDF has form fields, Fill forms lays them out as a checklist; flatten afterwards so the answers cannot be cleared. If it has no fields, either add them with Create form or type onto the page with Markup — the non-fillable form guide walks through both. For many copies from a list, Fill from spreadsheet.
Job 6: comment on it
Review comments should be annotations, not permanent marks: Comment & link writes sticky notes, highlights, boxes and links as standard annotation objects that the other person can reply to, edit or delete in any full reader. When the review is over, Flatten bakes them in or strips them.
When to go back to the source
Re-flowing a paragraph, changing a font, restyling a table, rewriting a page: these are document edits, and the document is the Word, InDesign or Google Docs file the PDF came from. If you do not have it, PDF to Word rebuilds an editable .docx from the PDF — layout-faithful or text-flow, your choice — on your device. Edit there, export, and convert back. That round trip is what “edit the whole PDF” realistically means, and it is free.
Everything above runs in the browser without the file leaving your device. A full desktop editor does more with typography and layout; for the jobs most people mean by “edit a PDF”, it is not needed.