For some reason the editor button creates a wrong link (like the one below) which requires users to login before they can download a certain file. If I manually get rid of the /administrator/ then everything works as expected. But I have no clue why the editor button automatically includes the /administrator/ part. Any ideas?

/administrator/index.php?option=com_joomdoc&task=document.download&path=Curricula/Curr_7_8.pdf

Hello,

I tested it and had same problem. This problem appears only if you have set some path to your joomla installation.
For example: localhost/joomla25/joomdoc/

path is: joomla25/joomdoc/
Code can not find administrator at start of that link, so it can not be removed.

How to repair this issue:
administrator/components/com_joomdoc/views/documents/tmpl/modal.php - line 63.

There is:
$prefix = '/administrator/';

Modify it to:
$prefix = JURI::base(true).'/';

Is this helpful for you and it solves your problem too?

apparently the problem is gone. I forgot to remove the jupgrade folder and move all files back to the root of my joomla installation after migrating my site.

But thanks for the quick reply.