There are several ways to make the Windows Explorer show full file extensions.
The most consistent method I like to use is the following:
Windows 7 and 8
- click Start to find a Search Box
- type Folder Options and select it
- click the View Tab
- find the option “hide extensions for known file types”
- untick it and hit apply
Windows 10
- click Start to find a Search Box
- type File Explorer Options and select it
- select the View Tab
- find the option “hide extensions for known file types”
- untick it and hit apply