[NTG-context] useexternaldocument with custom file type

[Jan U. Hasecke]

Am 23.04.20 um 19:25 schrieb Henning Hraban Ramm:
> 
>> Am 23.04.2020 um 16:36 schrieb Jan U. Hasecke <juh+ntg-context at mailbox.org>:
>>
>> Am 23.04.20 um 16:10 schrieb Vladimir Lomov:
>>> Please see the page about '\goto' command, it was written for a reason!
>>
>> Ok, with \goto{linkname}[program(target.doc)] it works.
>>
>> "works" means some PDF Viewers opens the right program.
> 
> 
> In the beginning, you could even start programs with program(...), but Adobe recognized soon this might be a security problem.
> 
> Nowadays, the “best” behaviour is when the viewer asks you if you really want to open such a link but then hands control to the OS.
> 
> Last time I checked, Adobe Reader even let you open hidden files from arbitrary paths.
> 
> Several other viewers just do nothing.

Yes this is not bullet proofed but I need it for internal usage. I think
we'll have many okular users.

juh