Yes. A document may be given a version number. Many
versions of the same document can be attached to a project ("Project Document") or a task ("File Attachment"). A document can be locked, in order to prevent other users from overwriting the actual online version (a good way to simulate a "Check In/Check Out" system). In that case, the other project assigned users can view the document, but they
can't overwrite the original version. However, they can modify the document and
save it with the same name, but with a different version number.
Sylvain Traversy
Customer Service and Documentation
support@aceproject.com
http://www.aceproject.com