How strong is a password protected PDF?
FileKiwi offers two kinds of protection, and they are not equally strong.
| Protection | What it does | How strong |
|---|---|---|
| Open password | The file cannot be opened or read without the password | Real encryption; strength depends mostly on the password |
| Block printing and copying | The file opens, but readers that respect PDF permissions refuse to print, copy text or edit | A rule readers follow, not a lock; some apps and tools ignore it |
The encryption is the standard PDF password protection with a 128 bit key (RC4, PDF security revision 3). It works in every common reader, but it is older than the AES 256 bit encryption some desktop PDF apps offer. A long password of several words is much harder to guess than a short one.
When to password protect PDF documents
Lock a PDF whenever it holds something you would not want a stranger to read if the email went to the wrong address or the shared link leaked.
- A tax return or bank statement going to your accountant.
- Medical results you send to a family member.
- Payslips that an HR team mails to each employee.
- A signed lease or ID scan for a landlord or agency.
Send the password through a different channel than the file, for example by text message or a phone call. Keep an unprotected original in a safe place, in case the password gets lost.
Before you lock the file
Finish all other edits first. Join documents with Merge PDF or shrink a heavy scan with Compress PDF, then add the password as the last step.
Fill in forms before protecting them, because form fields may become flat text. A PDF that already has an open password must be opened with Unlock PDF first; the tool tells you when that is the case.