If you are not going to ask the user for the name, where do you propose getting the name from?
In addition to Paul's link, if this is a mailmerge then you can name the individual documents from the merge data, using one of three merge tools available from my web site e.g.
http://www.gmayor.com/individual_merge_letters.htm or alternatively
http://www.gmayor.com/MergeAndSplit.htm makes it pretty simple to merge just one record named from the file, but someone has got to provide a name before you can save.