DOC and DOCX are both file formats for Microsoft Word documents. DOC is the older binary format used primarily in Word versions up to 2003. DOCX is the newer, XML-based standard introduced with Word 2007. Fundamentally, DOC files bundle all content and formatting into a single complex binary file. In contrast, a DOCX file is essentially a ZIP archive containing separate, human-readable XML files for text, styles, images, and other elements, alongside related resources. This structure makes DOCX inherently more open and modular.

Practically, DOCX is the default format for modern Word (2007 onwards), Google Docs, LibreOffice Writer, and many online collaboration platforms. For example, sending a DOCX file via email is often faster due to its smaller size compared to an equivalent DOC. A user editing a complex annual report with embedded charts in Word 2021 automatically uses DOCX, benefiting from features like advanced styling not fully supported in the older DOC format.

The primary advantage of DOCX is significantly reduced file size, enhanced data recovery options if the file corrupts, and better interoperability with other modern software. Its limitations include potential compatibility issues with very old Word versions (pre-2007) or niche legacy systems still reliant on DOC, though free converters exist. As the Office Open XML standard, DOCX drives broader accessibility and innovation in document processing tools, solidifying its role as the modern standard while DOC faces gradual obsolescence.