Folder Options and File Types
Every program in Windows that uses or creates files has an extension or file type associated for that program.
Some file types can be opened by several different programs. There are a lot of programs that open .jpg, .jpeg, .gif file extensions, including web browsers and all graphic programs.
Some file types are associated with only one program. Microsoft PowerPoint uses the file extension .pps. There are a lot of programs that are associated with only one file type.
Sometimes Windows may 'lose' the file association for a file. This can happen for various reasons. Sometimes a program can be installed that 'hijacks' a file type or association. If the program is uninstalled, then Windows just may not find another program to open the file.
If you need to re-associate a file type to a program, open Windows Explorer and click on Tools and on the drop down list, select Folder Options. Then click on the File Types tab. Using the scroll bar on the side scroll to the file type that needs to be associated with a program and click on it.
Screenshots of Folder Options/File Types
Once you have the file type located, then select it and change the program.