I've created a new lead magnet (pdf) to attract more subscribers. Is there any way to send the file to existing subscribers without them having to re-subscribe? I wouldn't want early adopters to miss out on the freebie and I'm concerned that sending a regular broadcast with an attached PDF (is this even possible?) might affect my deliverability since I don't have many subscribers and I also haven't emailed them a lot so far (I'm on a free CK plan, if that makes any difference)