Which PDF tool do I need?
To change what a page says, use the PDF editor (add text, white-out, sign). To turn a PDF into something editable, use PDF to Word for documents and PDF to Excel for tables and statements. For online forms that limit file size, use Compress PDF to size and choose 100 KB, 200 KB or your own limit. To change the paper size, for example Letter to A4, use Resize PDF. To lock a filled form so the answers can't be changed, use Flatten PDF.
Organise pages
Merge PDF joins files in the order you choose; Split PDF and Delete PDF pages take pages out; Organize PDF reorders them; Rotate PDF fixes sideways scans. None of these re-render the pages, so text stays sharp and searchable.
Privacy
Tools marked as running in your browser never send the file anywhere: it is read and saved on your device. That's why they also work on slow connections once the page has loaded.