bp_document_get_attachment_urls( [type] $attachment_id )

function bp_document_get_attachment_urls( $attachment_id ) {
	$urls = array( wp_get_attachment_url( $attachment_id ) );
	if ( wp_attachment_is_image( $attachment_id ) ) {
		foreach ( get_intermediate_image_sizes() as $size ) {
			$image  = wp_get_attachment_image_src( $attachment_id, $size );
			$urls[] = $image[0];
		}
	}

	return array_unique( $urls );
}