File Block in Microsoft Office prevents outdated file types from opening and can cause your file to open in Protected View via Trust Center.

Microsoft Office 2010 includes a new "Protected View" that, by default, will open all Outlook attachments and documents downloaded from the Internet in "read-only" mode.

Following that, go to the File Block Settings tab and make sure that the Open selected file types in Protected View setting is selected. If so, tick the Open checkbox of PDF Files.

PDF files are one of the most common formats used for sharing official documents, policies, medical reports, and financial ...