Most online PDF tools ask for your file so they can send it somewhere. I ask for it so I can open it. The editing engine runs in this tab: your PDF is read the way any program reads a file you opened, and nothing is posted to a server — there is no copy on the other end to delete afterwards, because one was never made. It also means no upload limit and no daily quota; the boundary is your own machine. I wrote this one down in full, under Guides on my page: "How to edit a PDF without uploading your file". 📄