DOC and DOCX extensions refer to the popular Microsoft Word file formats that have been part of its Office suite for a long time. DOC is the oldest file type and has been widely used prior to the introduction of the DOCX file format. DOC files are also known to be Word97-2003 files. DOCX file format was introduced with the launch of Word 2007 and is the default file format for saving word documents.

Routine users may not know the difference between the DOC and DOCX file formats, however, these two are different in several ways as detailed below.


Curious to know what is the difference between DOC and DOCX? Following is a list of differences between DOC and DOCX file formats.

The File Format Difference

The main difference between the DOC and DOCX file types is the underlying file format used for storing these documents.

DOC files are based on the Binary Interchange File Format (BIFF) that stores information as binary files. Data is organized in a DOC file as a collection of records and structures that are arranged in binary streams as described in MS-DOC file format specifications.

In contrast, a DOCX file uses the Office Open XML format that saves data in compressed XML files in ZIP format. If you want to examine the underlying structure of a DOCX file, simply unzip the .docx file to view its contents. You can rename the DOCX file extension to .zip and extract it to view its contents in a folder similar to any other files in the folder.

File Size Difference

Another difference is the difference in the file sizes of DOC and DOCX file formats. DOC files are stored as binary files that also contain related formatting and other styling information.

In contrast, DOCX stores the document in Open XML format that is finally stored as compressed ZIP format. This reduces the overall file size of DOCX as compared to the corresponding DOC file with the same content.

Following is a comparison of file sizes of DOC and DOCX files that have exactly the same content. As can be seen, the size of the DOCX file is significantly smaller than the equivalent DOC file.

Word Supportability

DOC files can be opened with any version of Microsoft Word starting Office 2003. However, DOCX files can only be opened with Word 2007 and lateral versions. If you still want to open DOCX files with older versions of Microsoft Word, you will have to install a compatibility pack for this purpose.

Functionality Difference

With every new release of Microsoft Word, the DOCX file format gets richer in features. New functionality is implemented only for DOCX file types and backward compatibility for incorporating the same in DOC file format is no more supported. This makes DOCX file format superior in terms of functionality as compared to DOC.

Implementation Standards

DOC files are stored as binary files whose complete file format specifications are still not available. Though Microsoft has opened some of the specifications as per its promise, still other word processing applications have difficulty in reading and writing DOC files.

In contrast, DOCX is based on open standards and implements XML file format as the basis. This makes it easy for others to adopt the same standard without any difficulty as XML is easy to read and write. Hence, no guesswork is involved in writing applications for processing DOCX files.


So, which one is the better option, DOC or DOCX?

Well, DOCX is the modern file format for working with Word documents and is more flexible as compared to DOC file format. Its Open XML implementation lets application developers easily write software to read and write these files. Shifting from DOC to DOCX is possibly one of the best decisions by Microsoft. Moreover, this XML-based implementation has allowed 3rd party software developers to introduce more dynamic and easy-to-implement APIs for working with DOCX files. Thus, DOCX is the obvious choice of use in this case.