How to Password-Protect a PDF

Why you might need this

Password-protecting a PDF makes sense any time you are sharing a document that should only be read by specific people: contracts, invoices, tax documents, ID scans, internal reports, or anything containing personal information. Without a password, whoever receives the file or finds it later can open it freely.

It is also the right move when sending documents over email, which is unencrypted by default. The password adds a layer of protection even if the email is intercepted.

Two types of PDF password (know which one you want)

PDF encryption has two distinct password types and most people only need the first one.

• Open password (Document Open password). Prevents anyone from opening the file at all without the password. This is what most people mean when they say “password protect.” The file is encrypted and unreadable without the correct password.
• Permissions password (Permissions or Owner password). Lets anyone open the file but restricts what they can do inside it, such as printing, copying text, or editing. This is useful for publishing documents you want read but not extracted. Note: permissions passwords are significantly easier to bypass than open passwords, and most PDF readers either ignore or can circumvent them. Do not rely on them for serious security.

For most use cases, set an Open password. That is what each method below configures by default.

Method 1: Mac Preview (free, built-in, best for Mac)

Preview is pre-installed on every Mac and handles PDF password protection without any additional software.

• Open the PDF in Preview.
• Go to File, then Export as PDF.
• Click the “Show Details” button if the full options are not visible.
• Check the box labeled “Encrypt” (or “Require password to open”).
• Enter your password and confirm it.
• Click Save. The exported file is now encrypted.

This is entirely offline. Your file never leaves your machine. It is the cleanest option available and there is no reason to use anything else if you are on a Mac.

Method 2: LibreOffice (free, best for Windows)

LibreOffice is a free, open-source office suite that includes a full PDF export feature with encryption. It works on Windows, Mac, and Linux. The install is about 350 MB and takes 2-3 minutes.

• Download LibreOffice from libreoffice.org (free, no account required).
• Open LibreOffice Draw (or Writer) and open your PDF file.
• Go to File, then Export as PDF.
• Click the “Security” tab in the PDF export dialog.
• Check “Encrypt the PDF document” and enter a password.
• Click Export. The saved file is password-protected.

LibreOffice Draw opens PDFs directly. If the formatting looks slightly off after opening, it does not matter, because you are exporting a locked copy, not editing the document.

Method 3: Microsoft 365 Word (if you already have it)

If your PDF originated as a Word document and you have a Microsoft 365 subscription, you can protect it during the Save as PDF step.

• Open the document in Word.
• Go to File, then Save As, then choose PDF as the format.
• Click “More options” before saving.
• Click the “Options” button and check “Encrypt the document with a password.”
• Enter the password and save.

This only works if you have the document source in Word format. If you only have the PDF, use LibreOffice instead.

Method 4: Online tools (SmallPDF, ILovePDF, PDF24)

Dozens of online tools will password-protect a PDF. The process is universal: upload the file, set a password, download the protected version.

The trade-off is significant: your file is uploaded to their servers. For public documents, marketing materials, or anything you would share freely anyway, this is fine. For contracts, financial records, ID documents, medical files, or anything containing personal information, uploading to a third-party server defeats the purpose of the protection.

If you genuinely cannot install software and need an online option, PDF24 is the most privacy-conscious of the major options and processes files on its servers in Germany. It is still an upload. Use it for non-sensitive files only.

Method 5: Adobe Acrobat Pro (skip unless you already have it)

Adobe Acrobat Pro, not the free Reader, can password-protect PDFs via File, then Properties, then the Security tab. It works well. It costs $20-$30 per month. If you are paying that subscription for other features, use it. If you would be subscribing solely for PDF password protection, it is not worth it. LibreOffice does the same thing for free.

Note: Adobe Acrobat Reader (the free version) can open password-protected PDFs but cannot create them. Many Windows users assume Reader and Acrobat are the same application. They are not.

Choosing a good password for your PDF

PDF open passwords are encrypted using AES-256, which is strong. The weakness is weak passwords. A short, common password can be brute-forced quickly with freely available tools.

• Use at least 12 characters.
• Mix uppercase, lowercase, numbers, and symbols.
• Do not use the name of the document, your name, or the recipient’s name.
• Share the password through a different channel than the document. If you email the PDF, share the password via text message or a separate communication.

The verdict

Mac users: open Preview, export as PDF with encryption. Done in under a minute, no install required. Windows users: install LibreOffice once, use it whenever you need this. The install takes two minutes and the tool is genuinely useful for other things. Avoid uploading sensitive documents to online tools regardless of how convenient they look.