Assigning library items as objects (or variable)

I would like to do the following with a compressed file:
1.) change file extension to zip
2.) Open the file (now a folder) and find all files within and assign them to an object or variable to be able to manipulate the files. Most of the containing files are of the same type and I can start from assuming they are all the same.

This problem is currently stopping all my work so I would be very thankful for any help/tips.

Thanks!

Changing the extension of a file does NOT change its contents.
The code will need to know the format of the content/internals of the file to be able to read it and get useful data from it.

Do you know how was the file created and what its internal format is?

Yes I want to open a files with file extension slx (Matlab Simulink files). And the internal files are mainly xml which are the ones I want to manipulate as a DOM or similar.