Compression is where online PDF tools most often disappoint. The two complaints people repeat are that the result is illegible, or that it's somehow bigger than the original — and in both cases you only find out after downloading it.
So this one shows you a sample page at the current and proposed settings side by side, before you commit. You can also name a target size — email attachment limits and government upload forms are where this actually matters — and let it find the quality setting that gets there.
The savings come from re-encoding the images inside the document and dropping unused objects. If the file is already well optimised, you'll be told so and handed back your original rather than a slightly worse copy of it.
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.