White Background Behind Signature

My office has a certificate that was created in Photoshop. In the past, I was able to save the certificate with different names as PDFs. I would then send these via MS SharePoint to the person who signs them. She would add her scanned signature using Acrobat without any problems. This time, the signature has a white background. It doesn't appear on my preview (Mac), but once the signer (PC) or I open it in Acrobat, it has the background. The signer said said she typically uses the sign option or watermark function, so it doesn't sound like anything has changed since the last time we did this in February.