You can download a PDF version of your email from the preview page (step 3 in the email creation process. Navigate to the preview page and look for the box containing the email subject line. On the right side of that box, click the Download PDF link to open the PDF copy for your email.
If you have already launched your email, no worries! On the sent email page, click on the Actions link next to the name of your email, and then click Make a Copy. Keep Edit this email selected, and then click Save. Click on Step 3 and follow the directions above to get your PDF.