Word

In short: Microsoft’s word processing program — the standard format (.docx) for documents in many companies and government agencies.

In more detail: The .docx format is technically a ZIP archive of XML files (Office Open XML), which is why it can also be programmatically generated and read without Word itself. Relevant for developers, for example, for automated document generation (contracts, invoices, reports).

In Depth

Internal structure of the .docx format

If you simply unpack a .docx file as a ZIP archive (renaming the file extension is enough), you find a folder structure of XML files: word/document.xml contains the actual text and formatting, word/styles.xml the style templates (Heading 1, Heading 2, normal text, etc.), other files images, metadata (author, creation date), and relationships between the parts (the _rels folder, which, for example, links which image is referenced where in the text). This open format (Office Open XML, standard since Word 2007) replaced the old, binary .doc format, which was only reliably readable with special, usually proprietary software, and whose internal format was never fully disclosed.

Programmatic use

For developers, this is relevant because Word documents can thereby be programmatically generated, read, or modified, without Word itself needing to be installed — useful for automated mail merges, generated invoices/contracts from templates (text blocks dynamically filled with customer data), or extracting text from uploaded documents for further processing (e.g. automatically searching application CVs for keywords). Libraries like python-docx (Python) or docx4j/Apache POI (Java) directly manipulate the underlying XML structure, without end users noticing anything — the resulting document opens completely normally in Word in the end.

from docx import Document
 
doc = Document()
doc.add_heading("Invoice", level=1)
doc.add_paragraph("Dear Sir or Madam,")
doc.save("invoice.docx")

Compatibility and alternatives

Despite the open XML format, there are still occasional display differences in practice between Word and alternative programs (LibreOffice Writer, Google Docs) — complex formatting, embedded objects, or unusual fonts aren’t always displayed 1:1 identically, especially with very old or very complex documents. Nevertheless, .docx remains the de-facto standard for text documents in business and government environments, similar to Excel for spreadsheets and PowerPoint for presentations — all three share the same underlying ZIP-plus-XML principle.

See also: Excel, PowerPoint, ZIP