When you say "a file is the same" do you mean the file name or the file contents?

This will compare based on the file name (UNTESTED):

#!/usr/bin/perl
use warnings;
use strict;


my $tempdir = 'c:/Temp/OneFile';
my $permdir = 'c:/Support/Files';

opendir my $TMP, $tempdir or die "Cannot opendir '$tempdir' $!";
my @onefile = grep -f "$tempdir/$_", readdir $TMP;
closedir $TMP;

if ( @onefile > 1 ) {
    die "Error: more than one file in $tempdir\n";
    }

if ( -f "$permdir/$onefile[0]" ) {
    rename "$tempdir/$onefile[0]", "$tempdir/$onefile[0]_1.txt" or die
+ "Cannot rename '$tempdir/$onefile[0]' to '$tempdir/$onefile[0]_1.txt
+' $!";
    }

exit 0;

__END__
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