1- In DSM Explorer, go under Control Panel - Configuration - Collect Tasks.
Right click on File Scan and select New...
2- In General tab, put a name for the collect task (ex: Collect .pst files)

3- In Windows Settings, click on "All files (*.*)" line and click on Remove Button in order to remove this line :
4- Enter *.pst (or choosen type of file) in text field and click on Add button to add the line
*.pst Include
5- Add directory C:\Windows\winsxs with Exclude option.
This directory is very big and could affect the performance.
Do the same for folder c:\windows\servicing as it could also be big on some servers.
6- If files to collect are non executable files (*.exe, *.dll), uncheck the option "Ignore non executable files"
7- Then assign this Collect Task to machines or group of machines
8- The File inventory of machines is small and contains only the specified files :