Answer
This isn't a configuration gap — it's a platform restriction. Due to security restrictions in iOS itself, the CRM Companion touch app on iOS devices only supports attaching image files (like JPEG) to business activities; other document types such as Word files can't be attached from an iOS device regardless of how the object-connection/mobile document settings are configured. If non-image document attachment from a mobile device is a hard requirement, that isn't achievable on iOS with this app — it would need to be done from the full application instead.