After a repository is crawled and files are indexed in the portal, users must be able to access the file from within the portal by clicking a link; this is the 'click-through' step.
Click-through retrieves a crawled file over HTTP to be displayed to the user. To retrieve documents that are not available via a public URL, you can write your own code or use the DocFetch mechanism in the IDK. If you handle document retrieval, you can also implement custom caching or error handling. Click-through links are gatewayed, so the content crawler can leverage user credentials and other preferences.