Hey, I've been using Sumatra PDF for quite a long time and I thought it was the time to give you some feedback; Hope they will help improving the app; here we go:
1. Name of the App: first of all it would be better if the name of the app was Sumatra Reader not Sumatra PDF because it can read lots of other formats and by adding the PDF to the name you emphasize that this app only can read PDF formats.
2. Book Shelf: It would be great if you could add the feature of adding bookshelf to the app so we could make our own bookshelf and add our books to it.
3. Builtin Dictionary: I think this app needs a builtin dictionary so you can find the meanings by right clicking on each word.
I simply see this app more than just a pdf reader and I do hope I can see more features in the near future.