Consult a beginner level Perl book ("Beginner Perl" for an example) to understand difference between file and file handle; currently selected file handle for print & its various forms.

...
my $write_dir = 'G:\research\sec filings 10k and 10Q\data\filing docs\
+1993\Clean';
...
opendir (my $dir_handle, $files_dir) || die "failed to open '$files_di
+r' <$!>"; 

 while (my $file = readdir($dir_handle) ) {  
...
     open my $file_handle, "/dwimperl/perl/1993/$file" or die "failed 
+to open '$file' <$!>";
         
         while (my $line = <$file>) {
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Actually use the file handle, not a file path, to read a line.

...
         print $write_dir "$file\n";
...
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The directory path is not a file handle but a string. If there is none such open file handle, print will fail. To write to a file for a specific file handle, open the file in write mode; use print FILEHANDLE LIST syntax; see print.

To copy or move files, see File::Copy.