A document revision can be compared with a local file. Select the revision you want to compare with the local file and choose Compare with local file… from the Edit menu. If a document is selected and not a specific revision, the [current] revision will be used to compare with. You can choose the local file using the file select window that pops up. This feature can be used to compare a revision in the ITP/MDK Repository with a Saved to… revision on the local file system that has been altered to fix a problem.
Refer to Compare Document Revisions for a remark on protected documents.