"If you change a filename extension,the file may become unusable"

Trouble:

“If you change a filename extension,the file may become unusable. Are you sure you want to change it?”

Warning can be seen in snapshot below.

The simplest way to fix such issue is to make the file extensions hidden. When you do that, windows will take care that the file extensions are not changed while renaming the file. To make the file extensions hidden, follow the below steps:

1. Open My Computer, go to Tools > Folder Options > View

2. Check the option “Hide extensions for know file types”.

3. Click Apply and OK.As seen in image below.

Method 2 :

Always provide the extension to the file explicitly as it was previously. For example if you want to rename a zip file from old name file1 to new name file2, make sure you rename the file from file1.zip to file2.zip. This means you have to type the extension manually.

We hope this helps to understand why the warning got flashed

Source: http://www.troublefixers.com