To answer this question, we have to take a closer look at how emails with attachments get filtered. In the SMTP process (delivering your emails) the first obstacle your attachment encounters is the receiving mail server (MTA). This is where your emails get checked for DMARC as well. For this part, having a properly set up DMARC policy + a great sender reputation can increase your deliverability.However, as we mentioned before, some recipients have extra spam filters. Not all will eliminate your attachments, but some have a taste of filtering out attachments they find spammy. In this case, DMARC is not going to help you: these spam filters do not check for email authentication. If this turns out to be a problem for you, you can either send a link to the PDF file or contact the spam filter about its malfunctioning.