A few thoughts might come to mind when someone receives a docx file for the first time. The first is "what is a docx file and how is it different from a doc file?" And another thought is "How do I open this docx file?"
So what exactly is a docx file? A docx file is a new file format Microsoft switched to for Word 2007 and later versions. The new format is completely different from the old "doc" file format. The old doc format was binary, which means it was just a bunch of ones and zeros that made no sense to the human eye unless it was decoded in another program (typically Microsoft Word).
One can describe the old doc format as proprietary, as it took reverse engineering by other programs to figure out how the document structure was laid out.
Microsoft came out with the newer docx format wich is an open XML format. This means the formatting, font, and table structures are denoted using XML tags - readable to the human eye. This is much more user friendly for other programs to parse or render the docx file.
But the file is still complicated, and it's actually a collection of files that make up the docx file. Those files are zipped together (compressed) to appear as one file, known as the docx file.
The upshot of all this is that Microsoft is making a step in the right direction to open up their file structure, but the new format is incompatible with older versions of Word. This is why we offer a simple online way of converting docx to doc so older versions can read docx files without buying or installing new software.
Here is a link to quickly convert docx to doc: