bp_document_get_preview_image_url( $document_id,  $extension,  $preview_attachment_id )

function bp_document_get_preview_image_url( $document_id, $extension, $preview_attachment_id ) {
	$attachment_url = '';

	if ( in_array( $extension, bp_get_document_preview_doc_extensions(), true ) ) {
		$get_preview            = $preview_attachment_id;
		$preview_attachment_id  = bp_document_get_meta( $document_id, 'preview_attachment_id', true );
		if ( ! $preview_attachment_id ) {
			$preview_attachment_id = $get_preview;
		}
		$document_id        = 'forbidden_' . $document_id;
		$attachment_id      = 'forbidden_' . $preview_attachment_id;
		$output_file_src     = bp_document_scaled_image_path( $preview_attachment_id );
		if ( ! empty( $preview_attachment_id ) && wp_attachment_is_image( $preview_attachment_id ) && file_exists( $output_file_src ) ) {
			$attachment_url     = trailingslashit( buddypress()->plugin_url ) . 'bp-templates/bp-nouveau/includes/document/preview.php?id=' . base64_encode( $attachment_id ) . '&id1=' . base64_encode( $document_id );
		}
	}

	return apply_filters( 'bp_document_get_preview_image_url', $attachment_url, $document_id, $extension );
}