Novice here..I know very little about file types, and am so overwhelmed. 
I have an Ai file of a simple text logo that I need to send to a client where they will then insert it on their bills/invoices, etc..and print from their printer. My question is, what format should I send this to them in? The Jpg file I sent was too small. This seems like it should be so simple, but I cannot seem to grasp it:( Any help is so appreciated.