Version control is maintained by allowing users to download and lock files. Downloading and locking a file ensures that users do not make simultaneous changes to a file and prevents file versions from branching. When a file is locked, it cannot be modified by another user and can only be unlocked by the person who locked it or a Workspace Administrator. Files can still be viewed when they are locked and all newly uploaded versions will be recorded in Version History tab.
Learn about:
Download + lock a file
Unlock a file
Files that cannot be locked
Download + lock a file
Under the Files & Discussions tab, click on a file name to view the file. Click on the drop-down arrow next to Download > Download and lock document.

Add optional comments, which will show on the file view page while the file is locked and click Download & Lock File.

After saving changes to the document, click on the Upload New Version button to upload and unlock the document. Select the file on your hard drive and add optional status or comments. The updated file is uploaded as a new version number.

Unlock a file
To simply unlock a file (and not upload a new version) navigate to a locked file and select the Unlock link.

Files that cannot be locked
Files in the Trash or with a Status of Read Only cannot be locked or replaced; they can only be downloaded. To interact with files in the trash, they will first need to be moved to a workspace folder. Files with a Read Only status will need to have the status changed by an administrator. Here is more information on document status