Why do you want such a thing from Notepad++?
Why not use something like Microsoft OneNote or Zim which were designed for the task?
Notepad++ displays all the chars in a file as they are. Hiperlinks by definition have displayable part and a hidden target part. Notepad++ is not designed to hide anything that exist within the file.
A plugin that relies on external database can do the trick. Either Open Selection will be fixed for you or you can adjust for your needs a tags based plugin that normally allow coders to Go To Definition of a tag. You will need to generate and maintain the tags database by yourself so your desired keywords will reference the txt files.