Can we do a "Save As"

You can go to My Spreadsheets. With the original document in the center, click the + key and select Duplicate Spreadsheet - you now have two documents identical documents. Do this at the beginning to keep the original and modify the copy. The files are not named, so you need to make the file clearly different - there is no Rev. Number or creation/modification time stamp that I can see. In the 'real' world you could Save As and not overwrite the original. Here, any change modifies the original in real-time.

You can rename a file in the "Documents View" (in this case, spreadsheets). Just click on the name and rename it.