Following up with FDE101, I used that print dialog box option to turn my booklet into a print-ready PDF, but my printer had major font issues and I didn't want to flatten the file in case he needed to make a change to the PDF. I wanted to do my file in reader spreads to post on digital formats but also be able to printout the booklet for distribution. Another approach that will work (very old school), if you have Acrobat Distiller you can print out you booklet using reader spreads and choose the booklet print in Affinity as a postscript. After the postscript has finished, take the file into acrobat distiller and convert to a pdf with your desired pdf profile preset. That's pretty much the way had to to do it back in the day with Quark to get pdfs before applications started enabling export to PDF. I suggested distiller because for some reason when you print to PDF from the print dialog box (MAC), it causes our RIP to crash and we have to restart the RIP and convert the problematic file to a JPG (ugh!).
I'm hoping Affinity will come up with a PDF setting where you can PDF to booklet from reader spreads to print ready spreads to take out the extra recreating documents because they have been setup in reader or printer spreads.