Liferay Documents and Media portlet lets an admin reinstate a previous version of a document as the document's new version.
For example, a document's Version History section lists the following versions (most recent at the top) of that document:
All versions, except the current version, have a Revert action that the admin can execute. If executed, the action reinstates the content of the older document version in a new version (e.g., 1.4) of the document. The new version of the document completely overwrites anything from the previous versions.