If there is only the one word "Paid," it's hardly a "document." And, what would be the purpose of faking it?
If you are asking if the paper itself is fake ... can't really tell. You can buy laid paper today, though it's not as common as a century and more ago.
If it is photocopied, it would likely be one-sided. If both sides were copied, hold it up to the light, and see if those grills (lines) match up exactly. The lines should be in the paper, not on it.