If you like creating and maintaining a library of free e-books, then here's a great way to add some to your collection. They're all from Microsoft, so the content is trustworthy and safe, although bear in mind that you're unlikely to find any books about Google or Apple in the collection! But if you're a Microsoft developer, or you use Microsoft Office, then there are dozens of interesting titles. All of which are available in PDF format and a couple of others too (mobi and epub).
I counted 360 different book titles here, so you could read one a day for an entire year (you deserve a break at Christmas!).
Just head to https://blogs.msdn.microsoft.com/mssmallbiz/2017/07/11/ and grab any that you like.