The most common time a user interacts with this file is when things go wrong.
(.shx for shapefile):
Check your AutoCAD Support Paths or consult your IT department to verify that no migration tool (like the Autodesk Migration Utility) inadvertently skipped legacy font folders. For further reading, review Autodesk Knowledge Network article ID: DL20331854 on SHX file management. aeccland.shx