Portable document format (PDF) files remain a popular choice for business documents ranging from contracts and forms to manuals and reports, so there's a good chance you need to open them often.

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.

Over the years, Adobe's PDF file type has become a universally accepted method for sharing digital documents. The format's cross-platform adoption means the documents can be viewed on almost any ...