2026-10-02
The reason to password protect a PDF is almost always that it contains something you would not want read by anyone who happens to get hold of the file — a contract, a payslip, a scan of an ID, a medical letter. That makes the usual way these tools work a little awkward: to protect the document you first hand an unprotected copy of it to somebody else's server.
Most online "protect PDF" tools, iLovePDF's and Smallpdf's included, work by uploading your file, encrypting it on their servers, and sending it back. That is a reasonable design and plenty of people are comfortable with it, but it means the unprotected file exists on a third party's infrastructure for at least a short time, which some employers, clients, and compliance policies simply do not allow. Others run into free-tier limits on file size or the number of tasks per day (check each tool's current limits), or do not want to create an account to finish a ten-second job.
Protect PDF does the encryption in your browser tab. The PDF is read, encrypted, and handed back to you as a download without your file being sent anywhere. It writes standard AES-256 encryption (the PDF 2.0 security handler), so the file asks for the password when you open it in current PDF readers, and the contents are genuinely encrypted rather than just flagged as protected.
You choose the password, and you can optionally switch off printing, copying text and images, and editing. If you restrict anything you can also set a separate owner password; leave it blank and a random one is used that nobody will know.
Be clear about what this tool does not do. It writes AES-256 only: very old PDF software (roughly pre-2010 readers, and some legacy print or archive systems) may not be able to open an AES-256 file, and some tools offer older RC4 or AES-128 options for exactly that case. If you need to support such software, check what your recipients use first. It does not do certificate-based encryption, it does not batch-process a folder of files, and it will refuse a PDF that already has a password — remove that first. Adobe Acrobat covers all of those cases, plus redaction and digital signatures, and a desktop app can comfortably handle files far larger than a browser tab is happy with. Protecting a PDF that carries a digital signature will also invalidate the signature, in this tool and in most others.
One thing is the same everywhere: if you forget the password, the file is gone. Nobody can recover it, including us — we never see it.
If the document is sensitive and you would rather it never left your machine unprotected, Protect PDF is the better fit, and it needs no account or upload. If you need legacy-reader compatibility, certificate encryption, batch processing, or redaction, use Acrobat or one of the established server-based tools instead.