pdf extension saving

I feel like I'm loosing my mind! I've been doing the same thing over and over and over and over for years and years and years....

When I create a document and name it: Invoice #21023 Waiver 2.11.21

I have ALWAYS just hit return and it would add .pdf to the end of it, AUTOMATICALLY.

Now all of the sudden...it's saving as a .21 document, which is obviously nothing... 

Is this a setting or a change to the software?

Ugh, I've done it for so long, I can't seem to remember to stop doing that and add .pdf to the end of all my documents. Remember, I've got a digital filing system that's been consisten for years - if I start putting the date somewhere else, it's going to make things very difficult for me to manage between clients.