What rule is that?
I use periods in Microsoft and Windows documents all the time, except they do not appear to be accepted when saving a pdf fromTurboTax.
Periods are more useful and easier to use than hyphens or whatever.
As a test I saved a pdf from TurboTax after interspersing 8 periods in the name.
All the periods came through but the last word in the name just before .pdf was deleted
There is something quirkier going on.
As Zeblon stated, relying on the (non-coder) user to notice the program didn't do what you told it to is not a very good way to respond to a bug that can cause data loss.
Things should work the way you expect them to work. Don't allow someone to enter characters without warning that the characters won't be accepted as inputted.
Can you point me to the rule in some lexicon of software omposition that says you can't use periods in filenames?
