A .doc or .docx file is a text document created with Windows Word.

This format contains not only plain text, but also additional formatting instructions.

You can open such a document with Microsoft Word without loosing any formatting information. However, it is also possible to use Microsoft Word Viewer or Libre Office for viewing or editing.  However, the formatting may change slightly. 

It is therefore recommended that you save objects as PDF when creating them and use this document for archiving.

Advantages:

- widely used

Disadvantages:

- proprietary