All Documents uploaded to the Workspace Documents app, have a status of Check-in or Check-out .
When a document is first uploaded, it has a default Check-in status, and may be downloaded and viewed, or Checked-out. Changing a document's status to Check-out locks the document such that no other user may upload another version of the document, or change the document's status to Check-in. Team members may, however, still download and view the version of the document that has been checked-out.
The team member that checked-out the document is the only person that can reset its status to check-in (other then an Administrator), and then upload the new version of the document. Once the new document is uploaded and saved, a new version of the document will be displayed in the Versions tab.