How to password protect a PDF in Adobe Acrobat — or free, without it
The free Adobe Reader cannot add a password. Paid Acrobat can: All tools, then Protect a PDF, then Protect with password. Or protect it free in your browser with AES-256, with nothing uploaded and no Adobe account.
To password protect a PDF without Adobe Acrobat, open Protect PDF, drop the file in, type a password twice and click Protect PDF. A copy encrypted with AES-256 downloads straight away. It runs in your browser, so neither the document nor the password is uploaded.
Most people searching this already have Adobe Reader open and cannot find the button. That is not you missing something. This page covers where the option lives in paid Acrobat, why Reader does not have it, and what the free tool here does differently from Acrobat, including the one Acrobat option it deliberately leaves out.
Can you password protect a PDF in Adobe Reader?
No. The free Acrobat Reader can open, sign and comment on PDFs, but it has no option to add a password. Protecting a file needs the paid Acrobat subscription, Adobe’s free online tool, or another app. Reader only asks for a password when someone else has already set one.
How do I password protect a PDF in Adobe Acrobat?
In paid Acrobat, open the PDF, select All tools, then Protect a PDF, then Protect with password. Choose whether the password is needed for Viewing or for Editing, type it, retype it and click Apply. Then save the file, because the protection is written when you save.
Adobe also has a free online protect tool. It works through Adobe’s website, which means the file goes to Adobe to be encrypted. For most files that is fine. For a payslip or a medical letter, it is one more copy on a server you do not control, the trade-off covered in is it safe to upload a PDF online.
Protect PDFAdd a password and encrypt the file.How do I password protect a PDF for free without Adobe?
Open Protect PDF in any browser, choose the file, type the password in both boxes and click Protect PDF. The encrypted copy downloads with _protected added to its name, and your original file is left as it was. There is no account, no install and no upload.
Open Protect PDF
Go to Protect PDF. It runs on your own device, with no sign-in and nothing uploaded.
Choose the PDF
Drop the file in or click to pick it. The password boxes appear once the file has loaded.
Type the password twice
Enter it in Password and again in Confirm password. The button stays disabled until both boxes are filled, and a mismatch is flagged before anything is encrypted.
Protect and download
Click Protect PDF. The encrypted copy downloads with _protected on the end of its name.
What is the difference between a Viewing and an Editing password?
A Viewing password, the open password, encrypts the document, so nobody can read a page without it. An Editing password only sets permission flags while the file still opens for anyone, and viewers are merely asked to honour them. Protect PDF sets the first kind only; with one password for both, there is no separate edit lock.
That omission is deliberate. Protect PDF puts the same password in both slots, so whoever can open the file can do anything with it, and there is no edit-only tier to set. An edit lock that any tool can ignore is not worth offering as security, which is the whole argument of what a PDF password actually protects. If you need others to read but not change a document, a password is the wrong tool. Flattening the pages to images makes a copy that is far harder to edit, though not impossible to retype.
How strong is the encryption?
Every file Protect PDF writes uses AES-256, whatever PDF version went in. We protected test files labelled PDF 1.0 through 2.0 and read each one back with a different PDF library from the one that wrote it. All came out AES-256, the wrong password was refused, and the title and author were encrypted too.
That last part needed fixing to be true. The underlying library chooses its cipher from the version number in the file’s header, and files that macOS Preview writes declare an old version, which used to get weak 40-bit RC4. Protect PDF now overrides that, so an old file gets the same lock as a new one.
The tool sets no minimum length. It refuses an empty password and nothing else, so it will encrypt a file with a single letter if that is what you type, and strong encryption under a one-letter password is still a one-letter password. Use a long passphrase, and keep it somewhere other than the email that carries the file.
How do I open a password protected PDF in Adobe Reader?
Open the file as usual. If it has an open password, Reader shows a password box before any page appears; type the password the sender gave you and the document opens. If it opens with no prompt but greys out printing or copying, it only carries permission flags.
Protect PDF’s output is the standard password-based encryption from the PDF specification. We have verified it with an independent PDF engine rather than inside Acrobat itself, so if a file ever refuses to open in Reader with the right password, that is worth telling us about.
I forgot my PDF password. How can I open it?
You cannot, if it was an open password. The contents are encrypted with it, and Protect PDF stores it nowhere, not even with us. Unlock PDF removes a password you still know; it does not recover a lost one. Keep the password in a password manager before sending the file.
A file that is already password protected is turned away rather than encrypted twice, with a message to unlock it first. If you want to change a password, run the file through Unlock PDF with the old one, then protect the unlocked copy with the new one. Removing a password has its own walkthrough.
Fillable fields, bookmarks and the document’s title survive protection, because the tool encrypts your file as it is rather than rebuilding it. Protect PDF sits with the other document-security tools in the security tools hub, and the shorter general walkthrough is how to password protect a PDF.
