Lock a PDF with a password, on your own device.
Add a password to a PDF in your browser, with nothing uploaded: AES-256 encryption, limits on printing and copying, and what those limits really do.
By Suraj Kumar4 min read
A payslip, a medical letter or a contract is about to go by email, and you would like it to need a password. Most PDF programs can do this, and so can several KeepSimp tools, in your browser, without the file going anywhere first. Here is how, and what a password on a PDF does and does not protect.
Two passwords, two jobs.
The first password is the one that matters: without it the file does not open. The pages are encrypted with it, and KeepSimp uses AES-256, the strongest kind a PDF offers. A program that does not know the password sees only scrambled data.
The second is optional. A file can ask programs not to allow printing, copying text and pictures, or changes, and a second password lifts those limits. They are a request rather than a lock: viewers are asked to respect them, and not every program does. Use them to make your wishes plain, not to keep words from being copied.
How to do it.
Open the PDF merger and add the file. Under More options, open Password and turn on Lock the merged PDF with a password. Type the password to open the file, then decide on printing, copying and changes. Press Merge PDF with the one file in the list and download it. To lock several files into one, add them all.
If you set limits and leave the second password empty, a random one is used and thrown away, so nobody can lift the limits, you included.
The same lock is in the PDF splitter (Lock every part with a password), the PDF compressor (Lock the result with a password) and the download options of the PDF editor. So a file can be made smaller and locked in one go, or signed and locked.
A strong lock needs a strong password.
With AES-256 the weak point is the password itself. A short word can be guessed by a program trying many each second; a long phrase of several unrelated words cannot. Do not reuse a password from an account.
Send the password by another route than the file: a text message for a file sent by email, or a phone call. A password in the same email as the attachment protects nothing.
Keep it somewhere safe. A lost password cannot be recovered, by KeepSimp or by anyone else, which is the point of the encryption.
Signed files and files that are already locked.
Locking writes the file again, so a digital signature in it stops being valid. If a document must stay signed, lock it before it is signed, or send it as it is.
To change a password, open the file with the old one and set the new one. In the merger and splitter the old password is removed; in the compressor and editor it stays unless you set a new one.
Neither the file nor the password leaves your device.
The file is encrypted in your browser and saved to your disk. The password is not stored or sent anywhere, and once the page has loaded it works without a connection.
Further reading
Topics: password protect PDF · add password to PDF · encrypt PDF · lock PDF with password · protect PDF free · password protect PDF without Adobe · restrict printing PDF · AES-256 PDF
A little less theory. A little more doing.
Try it on your own terms, with a free browser tool.
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