It is strongly recommended that users are warned to use the editor-specific save button to save document with all their changes. Classic Ctrl+S page/file save saves blank form, without any changes/edits made by user.
PDF editor is a great tool. It came just when I needed, I was about to fill a contract. Form with 20+ fields, my personal data, car data... I spent more than half an hour and then I saved it as it is intuitive - with Ctrl+S (same as "File - Save As). Then came the shock the next time I opened it, all the document was empty. God how angry I was.