The data files you work with have specific formats. The definitions of these data can be open (so called open formats) or proprietary formats, e.g. file formats of commercial vendors like Microsoft (.docx, xlsx). The open formats are in general maintained by the community and are, in general backward compatible. So if you open an older version in a newer application, it everything still looks as you stored it. Proprietary formats are often only kept backward compatible for a few versions. Also, they can go extinct. A well-known example is WordPerfect, which had been the market leader in word processing from the early eighties to the late nineties after which it got overtaken by word and was pushed out the market. Files with the extension .wp are very hard to open nowadays.

Hence, if you want your data to be sustainable, best use sustainable formats. At the UU we use the list of DANS as the preferred list of file formats.