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
 
