It may be that free PD books are significant in Pocketbook's native market but around here it's no big deal.
There's thousands high quality volumes right here on Mobileread. (18,000+)
https://www.mobileread.com/forums/ebo...r=&f=&genreid=
You can buy 27,000+ beautifully formatted and sorted ones on two DVDs for US$7.99 on ebay.
Or you can download them one by one from a dozen different sites.
Google alone boasts several million, though admitedly their's are of generally poor quality.