Protect a PDF with a password, limits and good habits
Published · Updated 2 min read
Protecting a PDF with a password prevents it from being opened without knowing the password, nothing more. It is useful for a document sent to a single person, provided you understand what this protection does, and what it does not.
What the tool does
It asks for a password of at least 12 characters, mixing three types among lowercase letters, uppercase letters, digits and symbols, which you type twice to avoid a typing slip. The resulting file asks for this password on opening. The encryption used is 128-bit RC4, an old method: it keeps the curious at a distance, but it is not suited to secrets you want to keep for a long time. The tool itself checks that the protected file opens with the password before offering it to you.
What the protection prevents
With a wrong password, the PDF reader refuses to open the document. That is the only effect.
What it does not prevent
- For anyone who knows the password, nothing is restricted: the tool limits neither printing nor copying text.
- A forgotten password cannot be recovered: keep an unprotected copy in a safe place.
- A protected file cannot be merged with another: remove the protection first.
Choose and pass on the password
Generate it with the password generator and keep it in a password manager. Send it through a different channel from the file: if the PDF goes by email, give the password by message or by phone. Otherwise, someone who intercepts the email has everything.
Protect last
A protected PDF is refused by the compression and cleaning tools, with a message asking you to remove the protection first. So do the protection as the very last step.
Test the opening
- Open the result in the reader the person will use.
- Try a wrong password: it must be refused.
- Keep the unprotected original.
- To remove the protection later, use Unlock PDF with the password, as in Open a protected PDF whose password you know.
For which documents
A contract, a payslip or a file sent to a single person: the password prevents anyone else from opening it. For secrets to keep a long time, this level of protection is not enough.
Frequently asked questions
- What password does the tool require?
- At least 12 characters, with three types among lowercase letters, uppercase letters, digits and symbols, typed twice.
- What encryption is used?
- 128-bit RC4, an old format: it keeps the curious at a distance, but is not suited to secrets to keep for a long time.
- Can you recover a forgotten password?
- No. Keep an unprotected copy in a safe place.
- How do you pass on the password?
- Through a different channel from the file: a separate message or a call. Otherwise, someone who intercepts the email has everything.