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 DC for free for seven days to add encryption options, encrypt with certificates or manage security settings to restrict editing, printing or copying. Acrobat Pro also lets you edit PDFs, organise PDF pages and convert PDFs to and from Microsoft Office 365 files, including Microsoft Word documents, PowerPoint presentations and Excel spreadsheets.