I want to remove "free trial" blue icon in lower left corner.

This might sound weird, but when I read a pdf document, in the lower left corner there is a blue icon or sign or whatever which says "free trial".

It is really annoying because every time I scroll slightly down the page, it momentarily disappears but comes straight back again. It is impossible to concentrate on the words when this blue image keeps flashing on and off and it is driving me crazy.

Is there any way to make this disappear?

Whose bright idea was this to put it there in the first place?