A secondary school has been using several English version office automation software packages which consists of a word processing software and spreadsheet software. This year the school paid and upgrade the office automation software packages so as to increase the use of information technology in teachin% to improve daily communication among its staff, and students and to computerized its student' attendance record system.
A teacher makes use of the upgrade word processing software to prepare an English test paper in school. However, he cannot open the document at home with his old version of word processing software. Explain why the teacher cannot open the document and suggest on the method the teacher can use to avoid the problem without any additional cost.