I also happened to replace my old Chromebook with a new one that will happily load Android apps, which lead me to the DriveThruRPG Library App in the Google Play Store or their website. It's a game changer and labor saver.
Although this review is of the Android App, it comes in a variety of flavors including Windows, Mac and iOS.
When you open the app, it asks you to log in. After that, it will sync up your purchased items in your library.
Clicking a name will do one of two things. If it is a single file, it will open it. If there are versions of pdfs or multiple files, it will give you a list.
The software can open the file one of two ways, in a browser on a Chromebook or within it's own build in pdf viewer.
The build in PDF viewer is sharp looking an responsive. The main difference between browsing in a browser or dedicated PDF viewer in Android is you loose the ability to print. That was probably a bridge too far for DriveThruRPG to create in their viewer. Other than that one missing feature it's robust, including smooth rendering, table of contents or bookmark views. It's nice.
All and all, I give it 5 of 5 Stars.
The only negative I could find was that the storage directory is not easily accessible for file access or manipulation. That isn't really a knock on DriveThru's Library app as this would happen with almost all Android Apps because of the way that a Chromebook emulates the Android Environment. If you want to get at the files directly, open them in the browser and save them to your downloads. The only reason I can think of to do this would be to back them up to media or a different cloud environment.