To create a strong password, increase the length of the password and add a mix of letters (both upper and lower case) and numbers. The addition of symbols can also increase password strength. When you enter passwords, avoid using personal information or common words found in a dictionary that can be guessed more easily.

When you open a PDF protected by a password, you’ll be prompted to enter the password. Type it in and click OK. Then the file will open.

When you protect documents with a password, people who enter the correct password can access the file or folder. A stronger security method is encryption, with common types being 128-bit key or 256-bit AES encryption. Encryption turns document content into unreadable cipher text. To decrypt the document, authorized users need a key, which is typically a password or a digital certificate.

When you use the Acrobat online tool to add password protection to a PDF file, it encrypts the file for added security. If you need more advanced PDF security, you can try Adobe Acrobat Pro for free for seven days to add encryption options, encrypt with certificates, or manage security settings and permissions to restrict editing, printing, or copying. Acrobat Pro also lets you edit PDFs, organize PDF pages, and convert PDFs to and from Microsoft Office 365 files, including Microsoft Word documents, PowerPoint presentations, and Excel spreadsheets.