findstr command to filter out files with given extension
If you want to get a list of all of the files in a directory other than those with a given file extension you can do so using the findstr command with a /vi switch.
dir | findstr /v ".pdf"
The dir command feeds in a directory list to the findstr search command and the /v switch filters the data with the value listed in quotes.
In this example the 'MyData' folder has 10 pdf files which are excluded from the list that is generated.