Parts list files contain custom blocks used to implement custom parts lists.
The path to the folder containing parts list files is in the system editor key Acad/M
Paths
DwgMask (Configuration file settings
gef@Paths@DwgMask).
By default, the key points to C:\ProgramData\Autodesk\AutoCAD Mechanical 2027\Acadm\Gen\Dwg\Msk.