Merge, split, reorder, rotate, sign, watermark and number PDFs; turn images into a PDF or a PDF into images; read the text out of one; edit its metadata; and password-protect, unlock or compress it.
Every one of these runs in the browser, and for PDFs that is the whole point. A contract, a scan of a passport, a signed agreement, a medical letter — these are the documents least suited to being uploaded to a free web service whose terms you have not read. The heavier jobs use a PDF engine compiled to WebAssembly, which loads on first use and then works with the network off.
Two of these produce a PDF rather than change one. A form can be filled in — text boxes, checkboxes, radio buttons and dropdowns — and saved either still editable or flattened, so the answers cannot be altered or read back out of the field. And an invoice can be built from line items with discount and tax by rate, in any currency — with India’s GST split into CGST and SGST (or UTGST) or IGST from the two states, or the VAT, GST, HST and PST of the EU, the UK, Canada and Australia, and reminders of what each country’s invoices must show — in five black-and-white layouts from a GST grid to an 80 mm receipt, and printed or saved without the document ever reaching a server, which is not a small thing for a document carrying a client’s name and a bank detail.
Pages can change size too: put every page on A4 or Letter with its text and links scaled rather than turned into a picture, crop a margin off each side, or trim the white edges off a scan, measured from the page itself.
And when an upload form says the PDF must be under 200 KB, it can be brought under exactly that: rewritten smaller first, with the text kept as text, and only if that is not enough, each page saved as a picture at the clearest resolution and quality that fit.
What must not be seen can be redacted for real: names, PAN, Aadhaar, phone and card numbers found and marked, or boxes drawn by hand, then every marked page redrawn as a picture with the boxes burned in — so nothing is left under them to select or copy — and the result read back to check.
A signed PDF can be checked too: whether the signed document is unchanged, whether anything was added after it was signed, and whose certificate signed it, with every signature checked in the page.