Word processing programs store documents in files. Spreadsheets are files. HTML pages are files. Databases are files. Your email in-box is a file.
Software is stored in files.
Everything on a computer is stored in files. I have 36,476 files of my own at the Statistics Department. Sometimes, the material to be stored is too complex to store in a single file and multiple files are used. Complex documents, for example, are often stored as parts in a collection of files. A book may consist of a title page in one document, a preface in another, a glossary in a third and each chapter in its own file.