Password Protect PDF
Add a password to a PDF so it requires that password to open.
How this works — please read
The libraries this site relies on for PDF editing (pdf-lib) don't support real PDF encryption. To still deliver a genuinely password-protected file, this tool renders each page of your PDF as an image, then rebuilds the file as a new, encrypted PDF from those images.
Trade-off: the resulting PDF's text will no longer be selectable or searchable — it becomes a set of image pages, similar to a scanned document. If you need to keep selectable text, this tool isn't the right fit; consider a desktop PDF application instead.