Perhaps you could take a screenshot of your HTML email, resize in a photo editor so it fits on a single page, and print that to PDF.
However, I have to wonder why your partner company is going to email a PDF version of what was originally an HTML email. Are they unable/unwilling to send the HTML email in it's original format?
If they want to control the email they send and just have an attachment from you with the details, then it may be better to design a PDF info sheet that is intended for that format vs. fitting the HTML email (square peg) into the PDF attachment (round hole).
I know these things can get tricky with partners and their requirements but just an alternative to consider!