Reading books has always been a common use case for tablets. Apple has iBooks, Google has Play Books, and both companies' respective platforms has any number of third-party options. Unfortunately, while Microsoft has embraced tablets since 2012, it never developed a solution for e-books, and to make matters worse, there have been few viable third-party solutions.
But soon, that will all change, as the company will begin selling books through the Windows Store. The report comes from MSPoweruser, which discovered the feature in an internal Windows 10 Mobile build, although it should be coming to PCs as well.
Once you've purchased the books from the Store, you'll be able to read them in the Edge browser, which, according to the report, will have a dedicated section for books. The browser received EPUB support back in November with build 14971, so it's clear that Microsoft has been laying groundwork for this feature.
It's not exactly clear right now whether or not users will be able to read these books on other platforms. For example, if one buys a movie or TV show from the Windows Store, it can't be watched on an Android or iOS device, as the Movies & TV app is only available on Windows.
They should be in EPUB format, so it seems reasonable to assume that they can be exported. Unfortunately, if this is the case, then don't expect your place in the book to sync. We'll likely find out more about the feature soon, as it's expected to show up in an upcoming Windows 10 build.