If you’re here then you’re probably having difficulty creating, inserting or opening a link? This page will attempt to explain how linking works (or not.)
In iOS, each application has 2 ‘sandboxes’. A sandbox is a special folder that an app has unfettered access too (to save files.) The first sandbox is ‘on device’ and the second sandbox is ‘in iCloud’. Generally speaking apps can only access files stored within their sandboxes. This is a security/privacy feature of iOS.
This means that iThoughts cannot link to a file in another app’s sandbox or a file in Dropbox/OneDrive/GDrive or even a file in a shared folder elsewhere in iCloud. Not cool!
However, with the introduction of the Files app on iOS11 the sandbox rules above got ‘blurred’ somewhat. It is now possible for apps to access files outside of their sandboxes - but only if the file is specifically selected by the user (using the iOS system file picker window.) An app cannot simply refer to a file by using its path. This is a security feature of iOS - stopping an app from seeing all your stuff whilst still allowing it to access specifically sanctioned files. Still not cool!
If you are getting errors when attempting to create/insert/open links - ensure that the ‘linked to’ map lives in one of the 2 app sandbox locations.
This makes linking to anything other than a website somewhat ‘restricted’ in Apple land. Unfortunately there is nothing I can do to address this…
In an attempt to keep things clear and simple, I have stretched the truth a little in the above. It is technically possible to create a link to a file outside of the sandbox by using something called a ‘security scoped bookmark’. Unfortunately this is something that will only work on iOS - so that same link would not then work on another device (iOS, Mac, Windows.) Security scoped bookmarks can also ‘go stale’ after a while (they’re not intended for long term storage.)