Example: Add fonts to pdf builder

add_filter( "wr_pdf_template_container_css", array( $this, "get_pdf_template_container_css" ), 10, 4 );

public function get_pdf_template_container_css( $css, $options, $payload ) {
	// Filter PDF Template Identifier
	if($option["identifier"]=="your_identifier") {
		$css = "YOUR CSS";
	}
	return $css;
}