Add apps to Share menu for iPhone
I would like to add an app to the Share function under the More option. The specific case...I have a reMarkable 2 device which can import PDF's and ePub files through it’s iOS app. In any app that could store or create one of these two formats (PDF's or ePub's), I would like to add the reMarkable app under the More option to Share documents. Can this be done and how is it done or could be done? Thanks.
[Re-Titled by Moderator]