As far as your concern. Lets say there are two Qlik Sense Apps,Which has same data source and all the measure and dimension are of same name between these two apps. Now App1 and App2 has 3/ different sheets each. Is your concern is to make a new App3 where these 3 and 3 sheet will comes together as 6 sheets ?
I've never heard of a tool that can merge 2 qvf documents. As far as I know you probably need to copy all the script from Data Load Editor from both Apps to the 3rd and then copy all the objects as it is into 6 new sheets from the Third App. Don't forget to stablish the same connection. My advice is to go to Apps and copy paste one of the two apps and then use the copied one to make the third app, then you'l save the process of copy the data+objects+connections into the Third application
You can even to the following: copy app 1 and use that copy and make a binary load of app 2 then you'll have all the tables in your datamodel in the copied file. After that it's only time to copy the objects
You can find an extension at Branch.qlik.com named Restore and Backup , you can make backup of your both qvf in json and then with the help of script editor merge the two JSON file and then create an new application and restore it. I am doing R&D on it , You may also try at your end , if there is any JSON developer or who knows JSON basic.
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