The document contains external references
The document under test is a part, assembly or drawing. 
Verification of external references.
Checks whether the locations are valid (whether a document exists), with the option to search for the referenced documents:
- only at the location listed in the document
- at the location specified in the document and based on the search rules specified in the SOLIDWORKS options.
The search level for the check can stop at the first level or extend to all levels.