No image shows when trying to create a stamp

When I try to create a custom stamp in Adobe Acrobat DC on Windows 10, the image I choose (pdf format) doesn't load. The image box just stays grey. I'm selecting an image I've saved into:

Program Files (x86)/Adobe/AcrobatReaderDC/Reader/plug_ins/annotations/stamps/ENU

(It's in this file that I found the Standard Business stamps I think are downloaded with Reader DC.)

I have the same image I want to upload on DC saved into this file, too: Users/name/AppData/Roaming/Adobe/Acrobat/DC/Stamps

Still no luck.

Can anyone suggest anything?

Thanks in advance.

Moved from Using the Community (which is about the forums) to the correct forum... Mod
To find a forum for your program please start at https://community.adobe.com/