Encrypt and then click Choose to begin encryption. If you have trouble with the above, then read the article titled Protecting your PDF Files in Adobe Acrobat 9.5. Decrypt a PDF using Adobe Acrobat Decrypt a PDF on Mac using Preview Decrypt a PDF on Mac by using Preview Decrypt a PDF file How to Decrypt a PDF file on Mac using macOS? How to decrypt a PDF on Mac — Decrypt a PDF file using Preview How to decrypt a PDF file in Mac OS 10.7 – 10.11 How to decrypt a PDF file in Mac OS 10.7 – 10.