Copy of invoice

My company purchased 3 licenses for Acrobat X Pro  around January of 2012.  We have recently become involved in a lawsuit, and need to prove we legitimately purchased this software.  Unfortunately we can't find the original invoice, and have no idea who it was purchased from as the employee who bought it no longer works here.  I have used the live chat over the last couple days to try and get some type of document that proves the software was obtained legally.  They directed me to this forum.  Would anyone be able to assist?  My case # from the live chat is 0218104471