Figured this out by doing the following (pagesubtitle is the name of the text field in the form):
$reportSubtitle = stripslashes($_POST['pagesubtitle']);
$reportSubtitle = iconv('UTF-8', 'windows-1252', $reportSubtitle);
Then print it out:
$pdf->Write (6, $reportSubtitle);
This will remove any unwanted slashes following apostrophes, as well as use the ‘iconv’ function to print special characters such as ™