The four kinds of PDF editor

Search for "PDF editor" and every result claims the same thing. Install a few and you'll find they do four different jobs, sold under one name. A lot of the angriest reviews on any PDF app come from someone who bought a form filler when they needed a full editor. The four jobs, and how to tell which one your task needs:

1. Annotators: they write on top of the page

An annotator treats the PDF as finished and lets you add a layer over it: highlights, comments, stamps, a drawn signature, shapes and arrows. The majority of free phone apps are annotators. So, mostly, are the viewers built into Chrome, Edge and Firefox, and Apple's Preview. (Preview also rearranges pages and fills form fields; it can't touch the document's own text, which is where the category ends.)

This is the right category more often than people expect. Reviewing a draft, signing a lease, marking up a student's work, filling in a scanned form by typing over the lines: all of it is annotation. The hard limit is that the original page is untouched underneath. An annotator cannot fix a typo in the document's own text, and a black box drawn over a name hides nothing from copy-and-paste. Plenty of paid apps are annotators priced like full editors.

2. Form fillers, for a PDF's interactive fields

A fillable PDF contains interactive fields, and filling them is its own job: the software reads the field definitions, takes your input, and stores it so the next program shows what you typed. The free Adobe Acrobat Reader is the reference tool here, and the browser viewers handle ordinary fields too. Storage is the part that fails often enough to have its own failure mode, the form that arrives blank, and the fix, flattening, is a form-filler feature rather than an editing one.

A form filler can't help with a form that's a scan of paper, because there are no fields to fill; that's an annotator's job, typing over the lines. And an annotator can't put values into fields that validate their input or that another program must read back as data. Filling and flattening are single-purpose tools here for exactly this reason.

3. Full editors: changing the page itself

This is what most people picture when they say "edit a PDF": click into the document's own text, change it, and have the result look like it was always there. Acrobat Pro defined the category; Foxit and Nitro (Windows and Mac) and PDF-XChange (Windows) compete in it on the desktop, and free options like LibreOffice Draw edit content with more rough edges. It is the hardest category to build, for reasons that come down to the format itself (no paragraphs, no reflow, incomplete fonts), which we've unpacked separately. Even the best full editors confine changes to a local area, and price alone won't identify the category: content editing is generally paid, but plenty of annotators cost money too.

There are two ways to change existing text, and a tool should say which it does. Desktop editors like Acrobat rewrite the page's own drawing instructions. Our editor covers the old line and re-sets it in the document's typeface. That's related to the annotator's white box, done carefully enough that the seam doesn't show, and its page states how it works: the original characters stay in the file unless you tick the option that rebuilds the page without them. Be wary of tools that do only the white-box trick without saying so.

4. Converters: taking the document somewhere editable

The fourth kind doesn't edit the PDF at all. It reconstructs the document in an editable format, where you rewrite freely, then export a fresh PDF. Recent versions of Word do this natively when you open a PDF; our converter does it in the browser. For heavy revision this beats everything else, since word processors reflow, spell-check and restructure in ways no PDF editor can. The cost is fidelity: the conversion infers structure the PDF never stored, and complex layouts come back changed. Converters are also the right choice for tables, which are easier to work with as a spreadsheet.

Where the work happens

Every category above also comes in three deployment flavours, and the difference concerns your file rather than the features. Desktop software processes documents on your machine and usually costs money. Upload-based websites are typically ad-funded or freemium, and they do the work on a server, which means your document travels, sits on that server for some retention window, and is subject to whatever the terms of service say. In-browser tools, the newest flavour and the one this site is built on, run the processing code on your own machine; the work happens locally and the file is never sent anywhere. With a flyer, who cares. With a contract, a medical record or anything under a confidentiality obligation, it decides which tools you're allowed to use at all.

Matching the tool to the task

• Comment, highlight, sign, stamp → an annotator. You likely have several installed already.
• Fill in a form with real fields → a form filler, and flatten before sending.
• Fix a typo, change a date, replace a name → a full editor, and expect small, local changes to work best.
• Rewrite paragraphs, restructure sections → a converter, then a word processor, then export.
• Remove something so it cannot be recovered → none of the above. That's redaction, which only resembles editing.

The categories blur at the edges, but only in one direction: a tool built for a harder category handles the easier ones. Marketing copy rarely says which way round the blur runs, so read any "editor" claim with the four jobs in mind.