With Docutain Pro you have the possibility to save your scanned documents as PDF on your device. This function gives you access to your documents independent of Docutain.
How to activate this function is explained in this article.
Go to main menu and tap on "Settings".
In the "Storage" section you can activate the function "Store documents on the device as PDF." by moving the slider to the right.
If you now scan a document, it will automatically be saved as PDF in the internal storage (files > on my iPhone > Docutain) of your device in a folder named "Docutain".