you can try below if you are not doing SSL validation,
untested though since I do not have permission to install Net::SSL module in my box

use strict;
use warnings;

use LWP::UserAgent;
use HTTP::Request::Common qw(GET);
use Net::SSL;

my $ua = LWP::UserAgent->new(ssl_opts => { verify_hostname => 0}, );

my $req = GET 'https://ptabdata.uspto.gov/ptab-api/documents';
my $res = $ua->request($req);

if ($res->is_success) {
    print $res->content;
}else{
    print $res->status_line . "\n";
}
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