Can't upload a photo to create my digital signature

Hi,

So I'm trying to create my digital signature right now on Acrobat. I have an existing PNG photo of my signature that I use on my home computer, and I'm trying to use it on Acrobat at work. According to the help page, I'm able to use PNG format - however when I go to browse for the file, the only file format option available in the drop-down menu is PDF. How can I get it to recognize a PNG, or any other image file?

I also converted it to a PDF but when I upload that I get an error message saying "Unknown error. Support Information: CGetSigningParams-3878."

Any help would be much appreciated as I have rapidly approaching deadlines and I need a ton of stuff signed pretty soon today. I'm on Windows 7.

Thanks!