How to Open a .P7s File. A P7s file is a digitally signed message designed to be opened in Microsoft's Outlook application.

If you see Word cannot open this file because it is larger than 512 Megabytes error on Microsoft Word, here's what you can do!

If you cannot open an Excel file and see Excel cannot open the file because the file format or extension is not valid error, see this post.

How to Open a PRJ File. The ".PRJ" file extension identifies a project file associated with multiple software programs. Microsoft Visual Studio saves development projects as PRJ files; AIMMS ...