if ($FileExt eq '.xlsx' || '.pdf'){

Unfortunately that doesn't work, although TIMTOWTDI (There's More Than One Way To Do It):

if ( $FileExt eq '.xlsx' || $FileExt eq '.pdf' )
    { print "Match!\n" }

if ( $FileExt =~ /^\.(?:xlsx|pdf)$/ )
    { print "Match!\n" }

use Quantum::Superpositions;
# OR
#use Perl6::Junction qw/ all any none one /;

if ( $FileExt eq any('.xlsx','.pdf') )
    { print "Match!\n" }
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Perl 6 supports Junctions natively, but note that Perl 6 is a related but different language that I wouldn't call production ready yet.

Update: Added a word.