TOPIC:

We offer Xamarin module only for Android and iOS.
Xamarin UWP is not supported.

-Entering text directly into the PDF document
Please check Add text to document (Windows)
-Bookmark features (Is this working and how)
currently we support adding bookmarks to the TOC (without UI). IS that what you want, or you want to save bookmarks in database?
-Undo Feature
This is currently not available, if you need this feature you need to contact sales department.

We do not support Xamarin UWP, so unfortunately we do not have any sample code to help you in this.

1- You need to give your sample project the same package name of the demo project/license (2625.RadaeePDFReader)

2- Make sure that the path is writable (has the Write access mode), if m_doc.CanSave returns false, this means that the document is in read-only mode and you cannot add/edit annotations.

You can check www.radaeepdf.com/documentation/windows/win8/

Please, don't use the forum as it's a reserved chatroom.
I shall invite you to split multiple questions in multiple posts: the forum shall be more readable by other users.

The forum is more than good but to make answering phase now and after the consultancy, let split your multi questions post in different posts.