The mask editor and the AMPARTLIST command use DSK files to implement special formatting options for custom parts lists.
The path to the folder containing parts list files is in the system editor key Acad/M
PathsDskPath (Configuration file settings gef@Paths@DskPath).
By default, the key points to C:\Users\Public\Public Documents\Autodesk\AutoCAD Mechanical 2025\Acadm\Gen\Dwg\Dsk