Power Query - Delete After this Row

No need for Power Query to grab the row number.

You can add a step by choosing Keep Rows - Keep Top Rows on the Home tab, just enter a dummy number and then adjust the code to:

= Table.FirstN(#"Changed Type",each [Header] <> "DeleteStartingThisRow")

You need a function in which the required transformations are done.

Next you can use this function for all (selected) files in the folder.

This will be done for you if you expand the binaries column from the navigation table with the files in your folder.

In this topic I explained this functionality, that was introduced with the November 2016 Update.

This will create some objects, including a "Transform Sample Binary" Query in which you shoud apply your transformations.

These transformations will be automatically propagated to the function that is used to expand all binaries.

However this will only work if you expand 1 type of binary (only csv or only xlsx or only ....).

If you have mixed extensions, then you need to create similar functionality yourself.

Let me know if this is the case and if you need more information on how to do that,

I may not be able to respond within a few hours though.

It looks like you are not using the Combine Binaries functionality how it's supposed to be used.

Just take a look at this video.