Incorrect application opening file when DOWNLOAD() is called

asmilie2b3

We are using NAV2013 (R1), and have an issue which is probably more a Windows thing than NAV. But I am scratching my head none the less. For a couple of users when they click a page action that uses the DOWNLOAD() function to download and open a file, the wrong application opens it. The file is of extention ".edi", and Windows is set to use notepad to open up files with that extention. But for some unkown reason Adobe Acrobat tries to open the file. Would anyone know where that setting is at all? I have loooked in the registry, in the programdata folder of the PC, the NAV client settings file but to no avail.