Every PDF carries a block of metadata most people never look at: who created it, with what software, and when. Documents exported from a work laptop routinely carry a full name and an internal template's title into the outside world.
This shows you everything that's in there and lets you edit or clear it before the file goes anywhere. Setting a real title is also worth doing for its own sake: it's what most PDF readers show in the window title bar and the browser tab, and an untitled document usually displays as a filename or, worse, as whatever the template was called.
The fields are the standard document properties — title, author, subject, keywords, and the creation and modification timestamps — plus whatever the producing application recorded about itself. Clearing them is a single action, and it's a sensible habit before sending anything out of an organisation.
Type into real form fields, or anywhere on a flat form.
Draw, type, or upload a signature and place it on any page.
Number the pages, with control over position and format.
Add DRAFT, CONFIDENTIAL or a logo across the pages.
Cut away white margins or crop pages down visually.
Combine files into one PDF and set the order before you merge.
Break a document into separate files by range or interval.
Drag pages into a new order, rotate or drop the ones you don't need.
Turn sideways or upside-down pages the right way up.
Pick pages to drop, visually or by range.
Keep only the pages you want as a separate file.
Combine JPG or PNG images into one PDF, with page size control.
Render pages to images at the resolution you choose.
Shrink a PDF with a side-by-side quality preview and a size target.
Add a searchable text layer to a scanned document.
Extract text as plain text or Markdown, in reading order.