A pamflet is something which has alot of information. It has a sense of a lot of pages.
A leaflet is a snigle piece of paper with information on it which can be distributed in numbers (alot of them).
A flyer is a leaflet, but it indicates that it goes into people's homes, through their letterbox. The other 2 do not.
An info bill = I have never heard of this. Maybe it's American.