Assembly: RevitAPI (in RevitAPI.dll) Version: 22.214.171.124 (17.0.1090.0)
DocumentVersion consists of two parts - a GUID and an integer. The GUID is updated as new elements are created in the document, but it is not necessarily changed whenever any individual change is made to the document. The integer is updated when the document is saved.
The GUID will change as changes are made to a model, so it should not be treated as a static value.
This class does not contain any time information - you cannot compare two DocumentVersions and know which document is newer. It can be used to tell whether a document has changed since it was last inspected. See GetDocumentVersion