Stamps in Acrobat

My previous workstation ran Windows XP. The most current of Acrobat Reader for that OS created custom stamps that did not have a white background - the image/linework/text would show, while any white space  was transparent and allowed whatever was under the .pdf to show.  I now have a Windows 10 workstation, with both the most current version of Reader and Acrobat DC.  Now any stamps I create (either from printing from my CAD program to .pdf or from an image file) has a white background. The only solution I've found to this has involved using Photoshop to remove the background, but I do not have that program.  I need to create custom stamps from a CAD drawing, so that I can mark up .pdf plans with custom symbols. Any suggestions that don't include purchasing new software?  These symbols are not black-and-white, either, I need to be able to do this in color.  Any help or ideas is greatly appreciated.  I'd even settle for a method to import my old stamps. I do still have access to the hard drive from my previous workstation, but the .pdfs from which I created those stamps have a background. I would need to be able to get to the stamps themselves, wherever Acrobat hides them. TIA