Hi Brent
Incidentally I had a similar requirement to display a PDF file after the user clicks on a link in the Survey
I have managed to solve this by putting an HTML link to the file in the survey:
concat('<a href="file:///storage/emulated/0/ArcGIS/My Surveys/549c05bae0f14e388000486ce4de950c/esriinfo/media/help.pdf" class="link external button button-raised button-fill color-blue">Demo</a>')
I am sure the class="link ....." can be simplified but it works the way it is at least 🙂
You will notice that 549c....950c refers to the item ID of the survey - so you will only be able to use that after you've at least published your survey once. Thereafter you can finalise your href links and it works pretty well - on Android at least... i suspect that if you venture to iOS devices the URL will be different but you can identify the OS by using "property('uri:deviceid')" function in a calculation column.
I will add this to my blog as well: https://community.esri.com/groups/survey123/blog/2018/06/08/html-links-for-survey123-to-just-about-a...
Regards