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, a dialogue will prompt you to enter the password before you’re able to see the file content. Type in the document open password and click OK to open the file. The document owner can also remove the password with an Adobe Acrobat Pro trial or subscription.

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, authorised 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 for Mac or Windows. The seven-day free trial lets you add encryption options, encrypt PDFs with certificates or manage security settings and permissions to restrict editing, printing or copying. Acrobat Pro also lets you edit PDFs, organise PDF pages and convert PDFs to and from Microsoft Office apps, including Microsoft Word documents, PowerPoint presentations and Excel spreadsheets.