How to Password Protect a PDF
Lock a PDF with a password using Word on Windows, free LibreOffice, Adobe Acrobat, or a browser - plus what Windows and Android cannot do for you.
The fastest route depends on where the file came from. If you wrote the document in Word on Windows, the password option is already sitting in the PDF export dialog. If you have an existing PDF and no paid software, the free LibreOffice suite will encrypt it offline, without uploading anything.
Windows itself has no built-in PDF password feature, so every method below means using an app you either already have or install once.
Pick the route that matches your file
| Method | What you need | Passwords it can set | Where your file goes | Best for |
|---|---|---|---|---|
| Word on Windows | Desktop Word you already have | Open password only | Stays on your PC | A document you wrote in Word |
| LibreOffice | A free download | Open password, permissions, or both | Stays on your PC | Any existing PDF, free and private |
| Adobe Acrobat desktop | A paid Acrobat plan or trial | Both, plus a choice of encryption level | Stays on your PC | Files you need to restrict as well as lock |
| Acrobat online in a browser | A browser; free use is capped | Open password | Uploaded to Adobe’s servers | A one-off file that is not sensitive |
| Acrobat app on Android | An Acrobat Premium or Pro subscription | Open password, saved as a separate copy | Adobe cloud storage | Protecting something away from a computer |
A PDF can carry two different passwords. A document open password is required to open and view the file at all, and it is genuine encryption. A permissions password lets anyone open the file but asks the reader’s software to block printing, editing, copying, or commenting. The distinction, and how each one is taken off again, is covered in more detail in our guide to removing a password from a PDF you own.
Word on Windows: the shortest route
If the document started life as a Word file, this is four clicks and needs nothing extra.
- Open the document and go to File, then Save a Copy (older builds and never-saved documents show Save As instead).
- Choose PDF in the file-type list.
- Select More options, then the Options button in the dialog that opens.
- Tick Encrypt the document with a password, then enter the password twice and save.
Microsoft’s own description of the checkbox is direct: “To restrict access so only people with the password can open the PDF, select this option.” It sets an open password and nothing more: there are no permissions controls.
Two caveats worth stating plainly. Microsoft documents this option in the Windows desktop Word section of its guide to saving or converting to PDF in Office desktop apps, and does not list it for Excel or PowerPoint. And the password box will be grayed out if the ISO 19005-1 compliant (PDF/A) box in the same list is checked. That is not a bug: PDF/A is an archiving standard, and the standard does not permit encryption, so one file cannot be both. Clear the PDF/A checkbox and the password option comes back.
LibreOffice: free, offline, and it handles existing PDFs
LibreOffice runs on Windows, macOS, and Linux, costs nothing, and never sends your document anywhere. If you are already leaning on free tools for this kind of work, it sits alongside the approaches in our roundup of ways to edit a PDF without paying for Acrobat.
To protect a document you are authoring, go to File > Export As > Export as PDF, open the Security tab, and select Set Passwords. You can set an open password, a permission password, or both. To protect a PDF that already exists, open it in LibreOffice Draw first, which is the component that opens PDF files, then use the same export path.
LibreOffice is also refreshingly honest about the limits of the second password. Its help page carries this warning: “The document permission restrictions set by password will be observed only by PDF readers compliant with the version 1.5 of the format. Thus, in older PDF readers, the restrictions may have no effect.” Treat a permissions password as a request that readers may honor. Only the open password is real encryption.
Adobe Acrobat: both passwords and a choice of encryption
Acrobat gives the most control, and it needs a paid plan or a trial. The free Acrobat Reader cannot add password security at all.
In the current desktop interface the route is All tools > Protect a PDF, then Protect with password in the left pane. Choose whether the password is required for Viewing or for Editing, type it twice (a strength indicator rates it weak, medium, or strong), and select Apply. Older builds put the same feature under Tools > Protect > Encrypt > Encrypt with Password, and both wordings are still in circulation, so use whichever your copy shows.
The fuller dialog, listed under ADVANCED OPTIONS as Encrypt with Password, is where you get both password types at once plus a Compatibility dropdown that decides the encryption. Adobe’s page on securing PDFs with passwords describes the choices roughly like this, although the exact labels vary between builds:
| Compatibility setting | Encryption applied | Who can open it |
|---|---|---|
| Acrobat 6.0 and later | 128-bit RC4 | Acrobat 6 and newer |
| Acrobat 7.0 and later | AES with a 128-bit key | Acrobat 7 and newer |
| Acrobat X and later | 256-bit AES | Acrobat X and newer |
Adobe’s guidance is to pick a version equal to or lower than the recipient’s Acrobat or Reader. Stronger is not automatically better here: a file encrypted for Acrobat X and later cannot be opened by Acrobat 7.
In a browser, or on an Android phone
Adobe runs the same feature on the web. On the Acrobat web home page, look for Edit, then Protect a PDF; there is a standalone tool page as well. The flow is the one you would expect: drag and drop the PDF, enter and confirm a password, select Set password, then download the protected file. Adobe’s password protect PDF page states that “your file will be securely handled by Adobe servers and deleted unless you sign in to save it.”
Two honest caveats. The document leaves your machine, which rules this out for anything genuinely sensitive. And Adobe classifies password protection as a premium online tool rather than a free one, so free use is capped rather than unlimited - check Adobe’s current FAQ for the allowance before you plan around it.
On Android there is no system-level setting, on Pixel or on Samsung’s One UI, that password-protects a PDF. The two real options are the Acrobat mobile app, where Set password in a file’s overflow menu requires an Acrobat Premium or Pro subscription and can only set a document-open password, or Adobe’s web tool in the phone’s browser. The mobile app also behaves differently from the desktop: it writes a separate protected copy, named with a _protected suffix, into Adobe cloud storage and leaves your original file untouched. For anything sensitive or repeated, do it on a computer.
What Windows and Android will not do for you
Microsoft Print to PDF, Edge’s PDF viewer, and File Explorer all handle PDFs without offering any security setting, and Google Docs has no password option in its Download as PDF menu. Samsung Notes can lock notes inside the app, but its export choices - Samsung Notes file, PDF, Word, PowerPoint, image, and text - include no password step, so the PDF you export from it is unprotected.
When you genuinely cannot encrypt the PDF itself, wrapping it in an encrypted archive is a fallback. 7-Zip encrypts 7z archives with AES-256, deriving the key from your password over a large number of iterations. The reason this is a fallback rather than the recommendation: Windows File Explorer cannot create password-protected archives, and even Windows 11 version 24H2, which added handling for more archive formats, does not support operations on encrypted ones. Your recipient needs 7-Zip installed too.
Emailing an encrypted PDF is fine. Google’s list of file types blocked in Gmail covers executables and scripts, including when they are hidden inside archives and inside password-protected archives - encrypted PDFs are not on that list.
Choose a password you will not lose
There is no recovery path. Microsoft states it plainly about Office documents: “If you lose or forget your document password, Word won’t be able to recover it for you.” The same holds for an encrypted PDF, because that is a property of encryption rather than a policy anyone can override. So pick something strong but retrievable, along the lines of our guide to building a strong password, and store it somewhere you will still have it in a year, which is the practical argument for using a password manager. Then send the password to your recipient through a different channel than the file itself.