Sorry, I didn't notice it was your first post. Welcome to the forum LongDead! Be sure and check out all the free books here at mobileread
https://www.mobileread.com/forums/forumdisplay.php?f=126 that are ready to go for your Sony. You can also look a few forums down from that one and get many ePub books that will also work..... And here is a link to free ebooks from the Sony store
http://ebooks.addall.com/sonyfree.html . Be sure to check back on the Sony link as the book content changes. Also Kobo is a great sight for buying books
http://www.kobobooks.com/ and is often cheaper than the Sony site. Inkmesh
http://www.inkmesh.com is a great search site for free and paid books.
Instead of the Sony software, you might want to check out Calibre
http://calibre-ebook.com/ , it's free (donationware) and excellent.
And feel free to ask questions, we like them here...
