The Conga File Repository is a proprietary repository used to store documents generated with the Composer Link Service.
The repository is separate and not related to Salesforce Files and Notes and Attachments.
All documents generated with Composer Link Service are automatically uploaded to the repository and accessible with a link on the Document History object.
The repository works in the background and is not tangibly accessible to Salesforce admins or users.
All Composer documents stored in the repository expire by default after 547 days (a year and a half) from the initial document generation.