How the PDF tools work
Each tool opens in a workspace on your own device. You choose a file, see the pages as thumbnails, set the options and download the result. The work is done by your browser using open libraries, so there is no upload, no queue and no account. That is also why large files depend on your phone or computer rather than on a server.
Which tool should I use?
To send a smaller file, use Compress PDF or PDF Size in KB. To put files together, use Merge PDF or Image to PDF. To change text, use Edit PDF. To get editable text, use PDF to Word or, for scans, the OCR tools. To keep a file private, use Protect PDF. To remove a secret before sharing, use Redact PDF.
Getting a smaller PDF
Forms often ask for a file under 100 KB, 200 KB or 1 MB. Scans of many pages are the biggest. Shrinking turns each page into a compressed picture, so choose a target size and check the result. If the text must stay selectable, use the tidy only mode, which saves less.
Your files stay private
Because processing happens on your device, the PDF is not sent anywhere. You can check this yourself with your browser's network panel. Read the how it works page for a step by step way to verify.