DOC vs DOCX: What Changed and Does It Matter?
Published on March 13, 2026
DOCX replaced DOC as the default Word format in 2007. The main differences: DOCX files are smaller, use XML internally instead of binary data, and handle complex formatting better. Unless you are working with files from Word 2003 or earlier, you are already using DOCX.
File Structure
DOC files store content in a proprietary binary format. The entire file is one opaque blob that only Microsoft Word could fully parse. DOCX files are actually ZIP archives containing XML documents, images, and style definitions. You can rename a .docx file to .zip, extract it, and read the XML directly. This structure makes DOCX files easier for other software to read and write, which is why Google Docs, LibreOffice, and Apple Pages all support DOCX natively.
File Size
DOCX files are typically 50-75% smaller than equivalent DOC files. The XML content inside a DOCX is compressed using ZIP, while DOC stores everything uncompressed in its binary container. A 10-page report with a few images might be 2 MB as DOC and 600 KB as DOCX. This adds up quickly when emailing documents or storing thousands of files.
Formatting and Features
DOCX handles modern Word features that DOC cannot represent: SmartArt, advanced chart types, certain table styles, and content controls. If you save a DOCX as DOC, Word will warn about features that will be lost or degraded. The reverse conversion (DOC to DOCX) preserves everything since DOCX is the superset. Any document created in DOC format can be converted to DOCX without losing content.
When You Still See DOC Files
DOC files show up in three places: legacy corporate systems that never migrated, government document archives from the 2000s, and email attachments from people running very old software. If you receive a DOC file, Word, Google Docs, and LibreOffice will all open it fine. There is no practical reason to keep saving in DOC format today.
Converting Between Formats
Open the DOC file in Word, Google Docs, or LibreOffice and save as DOCX. That is the most reliable method. Going from DOC/DOCX to PDF is also common when you want a format that looks identical everywhere. Our Word to PDF converter handles both DOC and DOCX files directly in your browser.
Related reading: RTF vs DOCX compares the lightweight Rich Text Format, ODT vs DOCX compares the open-source alternative, PDF vs DOCX covers when to use each document format, PPT vs PPTX covers the same format transition for PowerPoint, and CSV vs XLSX compares spreadsheet formats, and TTF vs OTF compares font file formats, and Pages vs DOCX compares Apple and Microsoft word processing formats.