Remembering to Save As is always a hassle. There is an easy way to make sure you never save over a document instead of Save As. Just open a copy of the file. To open a copy, first open up an Office program. Then Go to File, and Open. Here you will be presented with recently opened files or pinned files. Right click on the file you would like to open as a copy. Then simply select Open a copy below Open. A new window should appear titled Document2. This is a copy of the file you opened. When you are done making changes save [CTRL] + [S] the file with the desired new title.
Knowledgebase Article: http://helpdesk.etown.edu/helpconsole2012/KB/default.aspx#pageid=open_a_copy