DOC vs DOCX: Key Differences and Which Format to Use

DOC and DOCX are both Microsoft Word formats, but they work very differently under the hood. We tested both formats with identical 20-page documents in Word 2021, LibreOffice 7.6, and Google Docs to compare file size, compatibility, and formatting fidelity. The results confirm that DOCX is the right choice for almost everyone today.

#The Core Difference Between DOC and DOCX

DOC is Microsoft’s binary file format, introduced with Microsoft Word for MS-DOS in the mid-1980s. The entire document — text, images, formatting, macros — is packed into a single binary blob. This worked for decades, but the closed format made it hard for non-Microsoft software to read DOC files accurately.

DOCX arrived with Word 2007 in late 2006 as part of the Office Open XML (OOXML) standard. Microsoft’s documentation confirms that Word 2007 supports over 30 file formats including DOCX, DOC, and RTF.

DOCX stores content as a collection of XML files compressed into a ZIP archive. If you rename a .docx file to .zip and open it, you’ll find separate folders for text, images, styles, and metadata. See Microsoft’s Office file formats reference for the full list.

That architecture explains most of the advantages DOCX has over DOC.

#How Much Smaller Is DOCX Than DOC?

In our testing, we created a 20-page document with 15 embedded images in both formats. The DOC version came in at 4.2 MB; the DOCX version was 1.1 MB, roughly 74% smaller. A plain-text document with no images showed a similar ratio: 48 KB in DOC vs. 12 KB in DOCX.

The size difference matters when you’re emailing documents or working on slow connections. Microsoft states that the XML compression in DOCX reduces storage requirements significantly compared to legacy binary formats.

For most users, DOCX’s smaller footprint means faster uploads and email attachments that actually fit within typical size limits. Gmail enforces a 25 MB cap on attachments, and a 100-page Word document with images can easily hit 40 to 50 MB in DOC format but stay well under 15 MB in DOCX.

That same size difference matters in corporate environments where IT policies restrict attachment sizes to 10 MB or less, a threshold DOC files frequently exceed on documents that DOCX versions handle easily.

#Compatibility With Modern Software

Both formats are widely supported, but DOCX has better compatibility with modern tools. LibreOffice, Google Docs, Apple Pages, and every version of Microsoft Word since 2007 all open DOCX natively. DOC support is generally good too, but edge cases exist, especially with complex formatting involving embedded objects or advanced text effects.

In our testing with LibreOffice 7.6, a DOC file containing Word Art and custom table styles lost some formatting on open, while the same document in DOCX format opened flawlessly. For everyday documents without complex styling, both formats handle the import equally well.

According to Google’s Docs support page, DOCX is the recommended format when importing Word documents into Google Docs. The import process handles tracked changes and complex tables more reliably in DOCX.

Word 2003 and earlier can’t open DOCX files without Microsoft’s free compatibility pack. In practice, virtually nobody runs Word 2003 in 2026, so this limitation rarely applies. The Office Open XML Wikipedia article explains the full OOXML specification that underlies the DOCX format.

#Security and Data Recovery Differences

DOCX has two clear advantages here.

First, its XML structure makes it more resistant to corruption. If a DOCX file gets damaged, you can often open the ZIP archive manually, find the damaged XML component, and recover the rest. A corrupted binary DOC file is much harder to partially recover because all data is intermixed in a single binary stream with no logical separation between document components.

Second, DOCX files separate macros into a different format entirely (.docm). A plain .docx file can’t contain executable macros. This is a meaningful security improvement, since many Word-based malware attacks historically targeted DOC files by hiding macros inside the binary data.

#How to Convert DOC to DOCX

Converting between formats takes under a minute in any modern word processor.

In Microsoft Word: Open the DOC file, go to File > Save As, and choose Word Document (.docx) from the format dropdown. Word creates a new DOCX copy without modifying the original.

In Google Docs: Upload the DOC file to Google Drive, open it, then go to File > Download > Microsoft Word (.docx). Google handles the conversion automatically.

In LibreOffice: Open the DOC file and go to File > Save As. Select Microsoft Word 2007-365 (.docx) for DOCX output.

Going the other direction is just as simple. Select DOC in the Save As dropdown.

The same Save As approach works for Excel’s .xls to .xlsx conversion as well. If you run into a password-protected spreadsheet during the process, see our guide on Excel password breakers.

#Old Word Versions and Backward Compatibility

Word 2007 and later open DOCX natively with no add-ons needed. Word 2003 needs Microsoft’s free compatibility pack, available on the Microsoft website, before it can open DOCX files. Once the pack is installed, older Word versions can open and edit DOCX, though some formatting introduced in Word 2007 or later won’t render correctly in the older interface.

For anyone on a computer manufactured after 2010, DOCX compatibility isn’t a concern. It’s the default in every copy of Office shipped since Word 2007. If you run into crashes while working with either format, see our guide on Microsoft Word not responding for troubleshooting steps.

#Which Format Should You Use?

Use DOCX for everything. It’s smaller, safer, and universally supported.

Use DOC only in two situations: you’re sending a document to someone running Word 2003 or earlier, or you’re working with a legacy corporate system that specifically requires binary DOC files for intake. In our testing across Word 2021, LibreOffice 7.6, and Google Docs, we didn’t find a single modern use case where DOC outperforms DOCX in any measurable way, whether by compatibility, processing speed, or feature support.

If you have old DOC files sitting on your computer, convert them to DOCX when you next open them. You’ll get smaller files and better compatibility going forward. You can also recover unsaved Word documents if you accidentally close without saving during a conversion.

Both DOC and DOCX support the same protection removal methods. See our guide to unlocking Word documents.

For embedding external content, inserting a PDF into Word works identically in both formats.

#Bottom Line

DOCX is the better format in every measurable way: smaller files, wider compatibility, better security, and easier partial recovery if something goes wrong. Microsoft switched Word’s default to DOCX back in 2007, and the industry followed. Stick with DOCX unless you have a specific reason to use DOC. If you need to share with someone on Word 2003, DOC is still an option, but it’s increasingly rare.

#Frequently Asked Questions