Perl sctipt to convert file data format to another format

I need a PERL script that can find all the *.dat files under a certain folder and convert them to the new format. you will find an example attached what I want to convert the *dat files in the OLD folder to *dat files in the New folder with same folders structure I have a thousand of files with that I need the script to find them and convert them with the same way as I described above. Also at the end of the script I need the script to concatenate all the *dat files for all folders in one file and add a new column that contain the folder paths I need the source code of this script and I need it in Perl only and I need it ASAP