Add document as reference from different product/library

Ok, so we want to add a document as a reference document to a wtPart.  The search window comes up and I enter in the search tr* and it does not show anything.  The wtPart is in a product and the document is in a library.  How do I do that?  The user can see both the wtPart and the document.  We are on Windchill 10.2.