This tab is only available if Enable Project Documents is selected at Project Settings. If so, you can attach various documents to the project.
At the list of attachments, click Add, then select a document to attach it to the project:
For each listed one, click the file name to download that version or 
then:
•Edit Description to add or change the document’s description
•Download to obtain a copy of the latest draft
•Check Out to enable the document to be worked on. You will then be able to choose Undo Check Out to reverse the action and remove the checked out details
•Check In for a checked out document. Choose the version of the document to be checked in and change its description if necessary:
Files are checked out as draft versions for update and checked in once the changes are complete and the document is to become a published version. You can undo a check out if further changes are needed. The version number is updated automatically to reflect each version of the draft or published version, separate copies being kept at each stage.
•Delete to remove the attachment from the project record.
•Version History to view current and previous versions of the document:
Click a file name to download that version and click Delete to remove any selected versions except the latest one.