DOCX: what the file extension means

.docx, .doc, .xls, .ppt, and many more – anyone who regularly uses Microsoft Office programs will encounter many of these file extensions time and again. The file extensions are commonplace, but is a .docx file the same as a .doc file? And what does.docx actually stand for?

Just like a document with the ending .doc, a .docx file is a Microsoft Word text document. The format was introduced as a new standard for text documents with the release of Word version 2007. The aim was to establish a file format based on XML, which takes less storage space. The name “docx” is a combination of the previous .doc ending and the “X” from XML. The development of the file format for the other Microsoft Office programs is similar: For instance, the old Excel format .xls became the newer .xlsx format.

The main difference between the two file extensions .doc and .docx is the formatting – or how the file information is stored. A .docx file acts like a ZIP archive, which saves the content (texts and images) as XML and CSS data, and then compresses the file. When opening a .docx file, the content is then decompressed again. Overall, the storage and launch process for a .docx file is much faster – and far less storage space is needed for each file. Although this makes less of a difference today, it was quite important when it was introduced back in 2007, for example, for sending files by email.

Whether and when you can save a file in .doc or .docx format depends largely on the program or program version you wish to open the file with.

Generally, you can open a .docx file with the following programs:

• Microsoft Word
• OpenOffice
• LibreOffice
• Google Docs
• Word Viewer

When using Microsoft Word, however, the file ending matters. As of Word 2007, there won’t be any issues when opening .docx files. But older versions like Word 2000 or 2003 can’t open this format, unless you install the Microsoft Office Compatibility Pack. Due to the different formatting, it’s possible that a .docx document may not be displayed properly even after installing the extension.

Incidentally, the same is true for the reverse: If you want to open an older .doc file in Word 2007 or newer, display errors can occur especially for more complex text files like merged Word documents with lots of images and formatting.

Because .docx has been the standard in Word since 2007, there’s not much to keep in mind when saving your files. But to ensure that you are saving your document as a .docx file, you can check the format indicated from the drop-down menu “File Format” via “File” -> “Save As...”. Here, “Word document (.docx)” should be selected.