Paperform support e-signatures. When one is captured, it's stored in your Paperform results dashboard as an image link. Sometimes when you open the image directly from the dashboard it looks like a black page with nothing on it.
The background of the signature is transparent because Chrome recently decided to put a very dark grey background for transparent images viewed directly in the browser, so it comes out looking black. Don't worry, it's hiding there ;)
Try saving the file to you computer. Usually when you do this and open the file the background is a much friendlier color and the signature will stop hiding.