Techie help please

An ebay buyer claimed I had not sent an item & reported me to Paypal who are carrying out an investigation.
I sent the item by Recorded Delivery so took teh receipt to work today and scanned it on the photocopier & sent it to me here at home. It duly arrived in a PDF format.
I tried to attach it to my Paypal Dispute File but am getting the comment -
"Incorrect file extension. Please submit only files with the extension .gif, .jpg, or .png"
Does anyone know how I change the PDF into one of those?
Thanks

Posted By: South_West_Canary, Jan 21, 20:35:38