$ cat union.txt 
ABC Union
XYZ  Union

##</code><code>##

$ for i in agreements other; do for j in `ls $i`; do echo "*** $i/$j ***"; cat $i/$j; done; done
*** agreements/abc.txt ***
...
ABC Union
...
*** agreements/abc_xyz.pdf ***
...
XYZ Union and ABC Union
...
*** agreements/def.txt ***
...
DEF Union
...
*** agreements/pqrpdf ***
... temp data ...
*** agreements/xyz.pdf ***
.................. XYZ
   Union .............
*** other/dummy_empty ***

##</code><code>##

#!/usr/bin/env perl

use strict;
use warnings;
use autodie;

use File::Spec;
use List::Util 'first';

{
    my $union_file = 'union.txt';
    my @dirs = qw{agreements other};

    my $unions = get_unions($union_file);

    print "Unions to check:\n";
    print "\t$_\n" for @$unions;

    process_files($_, $unions) for @dirs;
}

sub get_unions {
    my ($union_file) = @_;

    open my $fh, '<', $union_file;

    my @unions;

    while (<$fh>) {
        chomp;
        y/ / /s;
        push @unions, $_; 
    }

    return [ sort { length $a <=> length $b } @unions ];
}

sub process_files {
    my ($dir, $unions) = @_;

    print "Prcessing directory: $dir\n";

    opendir(my $dh, $dir);

    for (grep /\.(?:txt|pdf)\z/, readdir $dh) {
        my $path = File::Spec::->catfile($dir, $_);

        print "\tProcessing path: $path\n";

        my $text = do { open my $fh, '<:crlf', $path; local $/; <$fh> };
        $text =~ y/ \n/ /s;
        my $found = first { -1 < index $text, $_ } @$unions;

        if (defined $found) {
            print "\t\tMATCH: $found\n";
        }
        else {
            print "\t\tNo matches found.\n";
        }
    }

    return;
}

##</code><code>##

Unions to check:
	ABC Union
	XYZ Union
Prcessing directory: agreements
	Processing path: agreements/abc.txt
		MATCH: ABC Union
	Processing path: agreements/abc_xyz.pdf
		MATCH: ABC Union
	Processing path: agreements/def.txt
		No matches found.
	Processing path: agreements/xyz.pdf
		MATCH: XYZ Union
Prcessing directory: other