Page Headers are a different issue from Table Header Rows .

Both would be applicable to your project.

In Page Headers, the default is to have a center tab and a right tab set in the Header style. For one column you could simply type and for the other press a tab before. If needed, you could insert a Table. If using Page Headers, see StyleRef Field to insert text from the body of your document dynamically in the headers.
You may want to look at Using Headers and Footers by Suzanne Barnhill, MVP.

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In the future, in this forum, when you need to change what you are asking about, please start a new thread. That will get you the best answers and make it easier for others using the forum to find information helpful to them.
Here you started out asking about inserting two text files side by side and now you are asking about headers. It is the same project for you, but it is a different subject for the forum.