Use this code example to prepend the text Entry ID: # at the top of the PDF file.

add_filter( 'frm_pdfs_export_content', 'add_extra_content', 10, 2);
function add_extra_content( $content, $args ) {
	$entry_id = '<p>Entry ID: #' . $args['entry']->id . '</p>';
	return $entry_id . $content;
}

add_filter( 'frm_pdfs_export_content', 'add_title_and_description_to_pdf', 10, 2 );
function add_title_and_description_to_pdf( $content, $args ) {
	$target_form_id = 385; // Change 385 to the ID of your form
	$form_id        = (int) $args['entry']->form_id;
	if ( $target_form_id !== $form_id ) {
		return $content;
	}

	$form = FrmForm::getOne( $form_id );
	return '<p>' . esc_html( $form->name ) . '</p><p>' . esc_html( $form->description ) . '</p>' . $content;
}

This code example removes the created_at date value from all downloaded PDF files.

add_filter( 'frm_pdfs_export_content', 'remove_timestamp_from_pdf_download' );
	function remove_timestamp_from_pdf_download( $content ) {
	$content = preg_replace( "/<p>((?!<\/p>).)*(\s)*Added on(\s)*\b.*?<\/p>/", '', $content, 1 );
	return $content;
}