A quick note before we start: ILoveConvert doesn't currently have a dedicated password-protection tool — this is a reference guide to how PDF passwords actually work, plus a genuinely free way to add one using software you likely already have.
Two Types of PDF Passwords
PDF security has two distinct password types that work differently and serve different purposes:
User password (open password): Required to open and view the file at all. Anyone who receives the PDF must enter this password before seeing any content. This is encryption — the file contents are mathematically scrambled and unreadable without the key.
Owner password (permissions password): Controls what the recipient can do with an already-open file — printing, copying text, editing, adding annotations. The file opens normally without a password, but certain actions are restricted. This is not true encryption; it is an honour system that PDF viewers respect but can technically be ignored.
How to Actually Add a Password (Free)
The most reliable free option most people already have access to is LibreOffice, which can open a PDF and re-export it with a genuine 256-bit AES user password:
- Open the PDF in LibreOffice Draw (or import it into Writer)
- Go to File → Export as PDF
- In the export dialog, open the Security tab
- Click Set Open Password and enter a strong password (see below)
- Export — the resulting file requires the password to open in any standard PDF viewer
Adobe Acrobat (paid) and most modern PDF editors offer the same capability under a similarly named "Protect" or "Security" menu.
PDF Encryption Strength
Modern PDFs support 256-bit AES encryption — the same standard used by banks and governments. This level of encryption is practically unbreakable with current computing technology. Older PDFs may use 40-bit or 128-bit encryption, which provides weaker protection.
When choosing a tool to password-protect a PDF, verify it creates 256-bit AES encryption rather than legacy 40-bit or 128-bit.
Choosing a Strong PDF Password
PDF passwords are vulnerable to dictionary attacks — automated systems that try millions of common words and combinations. Weak passwords are broken quickly. Choose a password that:
- Is at least 12 characters long
- Combines uppercase and lowercase letters, numbers, and symbols
- Is not a dictionary word, your name, a date, or a company name
- Is unique to this document (not reused from other accounts)
A memorable passphrase works well: three or four unrelated words combined — for example "Blue47Elephant!Coffee" is long, memorable, and practically impossible to guess or brute-force.
Sharing Password-Protected PDFs Securely
The most common mistake is sending the password in the same email as the protected file. If the email is intercepted, the attacker gets both. Best practices:
- Send the PDF by email, then share the password via a different channel — SMS, WhatsApp, or a phone call
- Use a password manager that supports secure sharing if you have one
- For very sensitive documents, consider using a secure file sharing platform with its own access controls rather than email
Removing a Password When You Know It
If you have the password and want to remove it from a PDF:
- Open the PDF in your browser (Chrome, Firefox) or PDF viewer
- Enter the password when prompted
- Use your browser's print function and choose "Save as PDF" as the printer
- The saved PDF will not have a password
What Password Protection Cannot Prevent
Password protection prevents casual unauthorized access, but it cannot prevent:
- Screenshots of visible page content
- Re-typing content manually
- Photography of the screen
For highly sensitive documents that must remain absolutely confidential, use a secure document portal with proper digital rights management (DRM) rather than relying solely on PDF passwords.