There are three main components here, let’s start from the top.
Front-end (MIT license)
The front-end source code is located at https://github.com/groupdocs-total/GroupDocs.Total-Angular and published to NPM e.g. https://email@example.com/viewer.
The front-end is Angular application that is typically located in
client folder (link). And here you can find viewer-specific components.
Front-end requires a back-end that will serve the content to display.
Back-end (MIT license)
The back-end code is a Web API that is serving the front-end (link). The back-end is using an engine to process the documents.
Engine (GroupDocs.Total license)
The engine is GroupDocs.Viewer for Java or GroupDocs.Editor for Java libraries that are performing the main work e.g. GroupDocs.Viewer converts documents to HTML/PNG/JPG/PDF formats.
To sum up:
The front-end and back-end code in the following repositories is open-source and you can modify it. The license is MIT.
The code in GroupDocs.Viewer and GroupDocs.Editor libraries is internal and you need GroupDocs.Total license to use these two libraries without trial limitations. You can’t directly modify the code but you can post request for the new features and report the bugs through this forum.