Want to automate inserting copy-pasting text from one file to another. iOS

This is for the iPad.

I’m new to coding. I did a little course in c++ some time ago on Udemy but thst’s it.

I have a project where I’m creating an html document. Creating the document involves grabbing text-A from plain-text file A in the Files app, placing that text-A into a particular section of copy-paste html code stored in plain-text file B in the Files app and then putting that as a whole unit into a specific point in the final html document. I’d like to automate this so all I have to do is prepare text-A and give some brief instruction as input as to where to insert it into the final html document.

I’m sure with enough study of Java in general I’d solve it, but could you tell me which topics and keywords in particular I should look at that would get me the knowledge to do this most quickly?