copy("$File::Find::name","C:\\temp\\/$_");

Where'd $File::Find::name come from? You didn't call File::Find's find(), you read a directory yourself. You're also calling copy() only once, so at best it would copy a single file.

You correctly use grep to filter the list of all filenames, but a) why use @allfiles there when you aren't interested in directories? and b) you join the list into a single string before assigning it to the @selected_files array, where it gets assigned to the first element. Then you never do something with @selected_files again..

Something else I noticed: you're opening the directory specified in $line, yet probably confusing the user by saying "Current directory contains [..]".

#! perl -w
use strict;

use File::Copy;
use File::Spec::Functions qw(catfile);

my $line = 'C:\08\00004DC4.013';

opendir MYDIR, $line or die "Could not opendir $line: $!\n";
my @allfiles = grep { $_ ne '.' and $_ ne '..' } readdir MYDIR ;
closedir(MYDIR);

my @files    = grep { !-d } @allfiles ;
my @dirs     = grep {  -d } @allfiles ;

print @files." files and ".@dirs." directories in $line\n" ;
print map "$_\n", @allfiles;

my @select_files = grep /\.rtf\z/i, @files;
for my $file (@select_files) {
    copy catfile($line,$file), catfile("C:\\temp", $file);
}
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