Just wanted to thank the OP for posting this. DW took this and ordered over two dozen, because homeschooling is still an option on the table.
And then, just after she finished downloading, her laptop crashed and burned. Naturally.
You're welcome. I bought 75.

I'm sorry to hear about the laptop, but even if it's complete toast, each PDF can be downloaded up to three times.
I'm a PDF nutcase. Every time I've bought a new worksheet-like book, say from Critical Thinking or the "[blank] for the Gifted" series, is scan each separate lesson/problem into a separate PDF. I've also done a ton of mazes and "brain booster" type of exercises this way. It makes it much easier to organize for me.
I've also started scanning in all of DS6's portfolio type of stuff (homework, etc.), minutes from TAT meetings, etc. I save emails and scanned letters to and from the school, as well as other historical documents, as PDFs, with file names starting with yyyy-mm-dd date format so it's easy to see the history.
What I've done with my whole "learning" folder, which contains worksheets and everything else related to the kids and their education, is put it into a TrueCrypt volume. That makes backing up the whole thing a snap, as simple as dismounting the volume and doing a file copy.