You don't have to subscribe to the LIT SUITE, but you'll be losing out! The current legacy versions of the apps (TrialPad 4.6.5, TranscriptPad 2.3.5, and DocReviewPad 1.5.10) will still receive technical support for a limited time but will not receive any more updates. If an update to the iPadOS or a third party service (e.g. Dropbox) breaks a part of an app it will not be fixed. All new features and improvements will only be going into the LIT SUITE apps.
