Many different spreadsheet programs use the dif file extension to enhance spreadsheet compatibility. To open dif files you will need a spreadsheet program that reads dif files. Dif files are much like txt files in their compatibility. The other great thing about dif files is that they can be edited in and out of spreadsheet programs. This means that if you would like to edit your dif file using a word processing program, you can accomplish this task as well as having it function in a spreadsheet program.
A great spreadsheet and word processing program that will open dif files is Open Office. The Open Office software bundle contains Open Office Calc which is a very compatibility spreadsheet program as well as Open Office Writer which is a word processing program. Both of these programs along with the other programs which come in the Open Office bundle, can open several different file extensions created by a multitude of different programs. Open Office is free to download and use for anyone. It is an open source software which means that it is updated by the internet community rather then a software company. Many people have contributed code to the Open Office program which also makes it much more stable then traditional office software.