There are many readers who usually write down observations on the margins of the books. That can also be done in text files. Proof of this is Notalon, a tool created to make it easier for users to make virtual annotations. Notalon is not only good for literary book readers, but also for students, who can use this notebook to take notes. It's over that taking notes at high speed that then one is not able to understand.
The notes are organized by a hierarchical tree that is located in the left panel. Comments annotated with Notalon are quickly found through your internal search engine. And to use Notalon you just have to write and create headings that serve as labels for your notes. Texts created with Notalon can be exported to a PDF document.
You can free download Notalon 32, 64 bit and safe install the latest trial or new full version for Windows 10 from the official site.