bp_document_get_preview_text_from_attachment( $attachment_id )

function bp_document_get_preview_text_from_attachment( $attachment_id ) {

	$data = get_transient( 'attachment_text' . $attachment_id );
	if ( false === $data ) {
		$file_open = fopen( get_attached_file( $attachment_id ), 'r' );
		$file_data = fread( $file_open, 10000 );
		$more_text = false;
		if ( strlen( $file_data ) >= 9999 ) {
			$file_data .= '...';
			$more_text  = true;
		}
		fclose( $file_open );

		$data              = array();
		$data['text']      = $file_data;
		$data['more_text'] = $more_text;
		if ( ! empty( $file_data ) ) {
			set_transient( 'attachment_text' . $attachment_id, $data );
		}
	}

	return apply_filters( 'bp_document_get_preview_text_from_attachment', $data, $attachment_id );
}