how to retrive data from an app which is not available on AppStore anymore

I took a lifetime subscription for one of the apps from AppStore and I used it for a few days and then I forgot about that app. When I wanted to reuse the app, it asked to update but the app is not available any more on AppStore. I hide some pics and documents using that app. Now I cannot access those data. How to get my data unhide with or without that app?