This is very helpful when you neither have manager access to the database, nor is your name in any of the document's reader field. You should have the database in your file system and there must be a role in the database ACL that is present in document's reader field.
Here is how we proceed:
1. From the file system, change the database extension from .nsf to .ntf and place it in the notes/data directory.
2. Now create a new database, using the above as a template. Choose the template from the list of templates given at the end of 'New Database' dialog box.
3. Since you have created the new database, you have manager access to it. So we now create a role in the new database, of exactly the same name as in the template database.
4. Assign yourself that role in the new database, and open it.
You now have access to all the documents.
Basically, whenever you inherit design from a template, you not only inherit the design but also the documents!