Hello,
We seek our clients satisfaction, and because of that, I suggest a couple of e-commerce platforms.
If your website idea, besides the PDF generation, is to start from a few static pages at the begining and add maybe one or two more weekly or monthly, I would suggest SilverStripe. If you have a clear image about the final site design and you are going to offer the usual payment methods (credit card, paypal,...), cool things can be done.
Otherwise, if you are planning to create a community around your website and you are willing to write tons of content and answer your readers comments and get feedback from all that, woocommerce/wordpress is your friend.
In any case, we would develop your idea from the platfom you decide.
Hope to hear from you and
Thanks in advance.