What relationships link your three tables? Are they like this?
Job::__pkJobID = Documents::_fkJobID
Documents::__pkDocumentID = Log::_fkDocumentID
For an explanation of the notation that I am using, see the first post of: Common Forum Relationship and Field Notations Explained
When you "click any particular log" what exactly are you clicking? How is that layout set up? Is this a portal to Documents placed on the Job layout?