Learn how to always open PDF files in Protected View in Word. Stop Word from opening PDF files in Protected View using GPEDIT or REGEDIT.

Q: Sometimes when I try to open a file or e-mail I get the message: "The selected file has an extension (PDF) that is not recognized by Windows Media Player but the player may be able to play it.

No matter your operating system, knowing how to combine PDF files is a good skill. We'll teach you the best ways to do so for Windows, macOS, or via the web.