Files with PDL extension can also be found as source codes written in the Perl Data Language.
PDL file extension - Perl Data Language file
What is pdl file? How to open pdl files?
File type specification:
The PDL file extension is also related to PERL Data Language and used for its script files. PDL gives standard Perl the ability to compactly store and speedily manipulate the large N-dimensional data arrays which are the bread and butter of scientific computing.