While working on a Windows machine, I needed a way to append to filenames for multiple files.

This is what worked for me:

1. Open the File Explorer and navigate to the folder where the files to be renamed are.
2. Hold the Shift key and right-click the explorer, then select "Open command window here".

3. In the command window, type the following script (where SUFFIX is to be replaced with the desired suffix):

   for %a in (*.png) do
     ren "%~a" "%~naSUFFIX%~xa"
   

4. Hit Enter, and enjoy.