The english formulation of your question is hard to understand. You will have to "open" the file to look inside of it whether by text editor or other means! Usually the question is: what subroutines does this module expect can be called by others? Look at the beginning statements:

 
our @EXPORT = qw(sub1 sub2);
our @EXPORT_OK = qw(sub3);
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Those are the subroutines that the module author expects will be called by others, the "public interface". It is possible in Perl to call other subroutines with a fully qualified name (package::sub5), but that isn't "playing by the rules". Past this simple advice, I don't understand your question - please explain more...