how to read multiple self-defined(.dd) files

I have some self-defined files(*.dd). And I have a self-defined function to transform .dd to struct. But it only woks for just one file. How do I do it with mutiple .dd files?

[Stephen23]

"How do I do it with mutiple .dd files?"

By folliowing the examples in the MATLAB documenation:

https://www.mathworks.com/help/matlab/import_export/process-a-sequence-of-files.html