How to Convert DOC to DOCX: Upgrade Legacy Word Files

Why Legacy DOC Files Still Exist

Microsoft introduced the DOCX format in 2007 with Office 2007. That was nearly two decades ago. Yet DOC files -- the older binary format used by Word 97 through Word 2003 -- remain surprisingly common. They persist in government archives, legal repositories, corporate document management systems, academic institutions, and the personal file collections of anyone who has been using computers since the early 2000s.

The reasons for this persistence are practical. Organizations with millions of archived documents cannot convert them all overnight. Legacy software systems that generate DOC files are still running in production. Templates created in the DOC era continue to be reused. And many users do not realize that the "Word document" they are working with is actually a format that has been functionally obsolete for a generation.

Converting DOC to DOCX is not just about modernizing file extensions. It unlocks real benefits: smaller file sizes, better compatibility with modern software, improved collaboration features, and future-proofing against the day when DOC support is finally dropped. This guide covers why the conversion matters, how to do it (individually and in batch), and what to watch out for during the process.

DOC vs DOCX: What Changed

The shift from DOC to DOCX was not a minor revision. It was a complete architectural redesign of how Word documents are stored.

The Architecture Difference

A DOC file is a monolithic binary blob. It contains everything -- text, formatting, images, macros, metadata -- in a single binary stream that follows Microsoft's proprietary Compound File Binary Format. Reading or modifying this format requires specialized libraries that understand Microsoft's internal data structures.

A DOCX file is actually a ZIP archive. Rename any DOCX file to .zip and you can open it with any archive tool. Inside, you will find:

document.docx (renamed to .zip)
├── [Content_Types].xml
├── _rels/
│   └── .rels
├── word/
│   ├── document.xml      (main document content)
│   ├── styles.xml        (paragraph and character styles)
│   ├── settings.xml      (document settings)
│   ├── fontTable.xml     (font references)
│   ├── media/            (embedded images)
│   │   ├── image1.png
│   │   └── image2.jpg
│   └── _rels/
│       └── document.xml.rels
└── docProps/
    ├── app.xml           (application metadata)
    └── core.xml          (title, author, dates)

This open structure means DOCX files are inherently more transparent, recoverable, and interoperable than DOC files. If a DOCX file becomes corrupted, you can often extract individual images or text by unzipping it and reading the XML directly. A corrupted DOC file is usually irrecoverable.

File Size Reduction

The XML compression in DOCX files typically produces files 30-75% smaller than the equivalent DOC. A 10 MB DOC file might become a 3-5 MB DOCX file with identical content. This matters for email attachments, cloud storage, and network transfers.

How to Convert: Step-by-Step Methods

Method 1: Microsoft Word

The most straightforward conversion uses Word itself.

Simple Save As:

1. Open the DOC file in Microsoft Word
2. Go to File > Save As (or File > Save a Copy)
3. In the "Save as type" dropdown, select "Word Document (*.docx)"
4. Choose a file location and click Save
5. The new DOCX file is created alongside the original DOC

Using "Convert" mode:

When Word opens a DOC file, it runs in "Compatibility Mode" (shown in the title bar). This mode disables features that are not supported in the DOC format. To convert:

1. Open the DOC file
2. Go to File > Info
3. Click "Convert" (next to the Compatibility Mode notice)
4. Word converts the file to DOCX format and exits Compatibility Mode
5. Save the file

This method upgrades the file in place, enabling all modern Word features. The original DOC file is replaced unless you save to a new location.

Method 2: LibreOffice (Free, Cross-Platform)

LibreOffice Writer handles DOC-to-DOCX conversion on Windows, macOS, and Linux:

1. Open the DOC file in LibreOffice Writer
2. Go to File > Save As
3. Select "Office Open XML Text Document (.docx)" from the format dropdown
4. Click Save

LibreOffice is an excellent free alternative for users who do not have Microsoft Word. It handles most DOC formatting correctly, though complex documents with advanced Word-specific features may need minor adjustments.

Method 3: Online Conversion

The document converter on ConvertIntoMP4 supports DOC to DOCX conversion:

1. Upload your DOC file to the DOCX converter
2. The tool processes the file and converts it to DOCX
3. Download the converted file

This method requires no software installation and works on any device with a browser.

Method 4: Command Line (LibreOffice Headless)

For automation and batch processing, LibreOffice can run in headless mode from the command line:

# Convert a single file
libreoffice --headless --convert-to docx input.doc

# Convert to a specific output directory
libreoffice --headless --convert-to docx --outdir /path/to/output input.doc

# Convert all DOC files in a directory
libreoffice --headless --convert-to docx /path/to/docs/*.doc

Method 5: Python Automation

For programmatic conversion:

import subprocess
import os

def convert_doc_to_docx(input_path, output_dir):
    """Convert a DOC file to DOCX using LibreOffice."""
    subprocess.run([
        'libreoffice', '--headless', '--convert-to', 'docx',
        '--outdir', output_dir, input_path
    ], check=True)

# Convert a single file
convert_doc_to_docx('report.doc', '/output/')

# Batch convert all DOC files in a directory
input_dir = '/path/to/docs/'
output_dir = '/path/to/output/'

for filename in os.listdir(input_dir):
    if filename.endswith('.doc'):
        convert_doc_to_docx(
            os.path.join(input_dir, filename),
            output_dir
        )

Batch Conversion for Large Archives

Organizations with thousands or millions of DOC files need a systematic approach to conversion.

Planning a Batch Migration

PowerShell Batch Conversion (Windows)

$word = New-Object -ComObject Word.Application
$word.Visible = $false

$docFiles = Get-ChildItem -Path "C:\Documents" -Filter "*.doc" -Recurse

foreach ($doc in $docFiles) {
    $docxPath = $doc.FullName -replace '\.doc$', '.docx'
    $document = $word.Documents.Open($doc.FullName)
    $document.SaveAs2($docxPath, 16)  # 16 = wdFormatXMLDocument
    $document.Close()
    Write-Host "Converted: $($doc.Name)"
}

$word.Quit()

Bash Batch Conversion (macOS/Linux)

#!/bin/bash
INPUT_DIR="/path/to/doc-files"
OUTPUT_DIR="/path/to/docx-output"

mkdir -p "$OUTPUT_DIR"

find "$INPUT_DIR" -name "*.doc" -not -name "*.docx" | while read -r docfile; do
  echo "Converting: $docfile"
  libreoffice --headless --convert-to docx --outdir "$OUTPUT_DIR" "$docfile"
done

echo "Batch conversion complete."
echo "Files converted: $(ls -1 "$OUTPUT_DIR"/*.docx 2>/dev/null | wc -l)"

For more on batch file processing workflows, see our batch processing files guide.

Handling Macros During Conversion

DOC files can contain VBA (Visual Basic for Applications) macros -- automated scripts that perform tasks within the document. Macro handling during conversion requires careful attention.

Macro Security Concerns

DOC files with macros are a significant security risk. Macro viruses have been a persistent threat since the 1990s, and legacy DOC files from that era may contain malicious code. Converting to DOCX strips macros by default because the DOCX format does not support them.

If you need to preserve macros, save as DOCM (macro-enabled document) instead of DOCX. The DOCM format clearly signals that the file contains macros, allowing security policies to handle it appropriately.

Conversion Options for Macro Files

Checking for Macros Before Conversion

In Microsoft Word:

1. Open the DOC file
2. Press Alt+F11 to open the VBA editor
3. Check the Project Explorer for modules and code
4. If modules contain code, decide whether to preserve (DOCM) or discard (DOCX)

Formatting Issues to Watch For

Most DOC-to-DOCX conversions are seamless, but certain formatting elements can shift during the process.

Common Issues

Font substitution: If the DOC file uses fonts not available on the conversion system, the converter substitutes similar fonts. This can change line lengths, paragraph spacing, and page breaks. Common victims: decorative fonts, non-Latin scripts, and organization-specific fonts.

Table layout changes: Complex tables with merged cells, nested tables, or precise column widths may render slightly differently in DOCX. Verify tables after conversion, especially in formal documents.

Page breaks and section breaks: The DOC and DOCX formats handle section breaks differently. Most conversions preserve them correctly, but unusual section configurations (different first-page headers, mixed portrait/landscape sections) should be verified.

Drawing objects: Older DOC files may use legacy drawing objects (AutoShapes, WordArt, text boxes) that are converted to modern equivalents. The visual result is usually identical, but the underlying object type changes.

Embedded OLE objects: Documents containing embedded Excel charts, Visio diagrams, or other OLE objects may not convert these objects perfectly. Verify embedded objects after conversion.

After Conversion: Next Steps

Verify the Conversion

After converting, open the DOCX file and check:

• Overall formatting and page layout
• Tables, especially complex ones
• Images (position, size, quality)
• Headers and footers
• Page numbering and section breaks
• Fonts (look for unexpected substitutions)
• Any embedded objects or charts

Update Templates

If your organization uses DOC templates, converting them to DOTX (or DOTM for macro-enabled templates) ensures that all new documents created from the template use the modern format.

Fix References and Links

Documents that link to other documents (via hyperlinks, fields, or references) may need their links updated if the referenced files have also been converted from DOC to DOCX.

Consider Further Conversion

With your documents in DOCX format, you now have a clean starting point for other conversions:

• DOCX to PDF for distribution and archiving -- see our guide on how to convert Word to PDF
• DOCX back to DOC if needed for legacy system compatibility -- the document converter handles this
• DOCX to other formats (HTML, Markdown, EPUB) using the document converter

For a deeper comparison of when to use PDF versus DOCX for different purposes, see our guide on PDF vs DOCX comparison.

Why Convert Now?

The case for converting DOC files sooner rather than later is compelling:

Declining support: Software vendors are gradually reducing DOC support. Google Docs converts DOC files to Google's internal format on upload. Newer versions of LibreOffice occasionally introduce DOC rendering differences. Microsoft itself has been encouraging DOCX migration for nearly 20 years.

Security: DOC files with embedded macros are a persistent security risk. Converting to DOCX strips macros, reducing the attack surface. Security policies that block DOC attachments in email are increasingly common.

Collaboration: Modern collaboration features (real-time co-authoring in Office 365, SharePoint, OneDrive) require DOCX. DOC files cannot participate in these workflows.

File recovery: A corrupted DOC file is often irrecoverable. A corrupted DOCX file can frequently be partially recovered by extracting its XML contents from the ZIP archive.

Future-proofing: DOCX is an ISO standard with multi-vendor support. DOC is a legacy format with no future development. The longer you wait to convert, the harder it becomes as supporting tools and expertise diminish.

Wrapping Up

Converting DOC to DOCX is a straightforward operation with outsized benefits. The conversion itself is simple -- open in Word and save as DOCX, use LibreOffice for free cross-platform conversion, or use the online DOCX converter for quick browser-based conversion. Batch conversion is equally straightforward with command-line tools or scripted workflows.

The real work is in the planning: identifying which files to convert, testing conversion quality on a representative sample, handling macro-containing documents appropriately, and verifying formatting after conversion. For small collections, this is a few minutes of work. For enterprise archives, it is a project worth planning carefully.

The result is a document collection that is smaller, more secure, more compatible, and ready for modern collaboration and distribution workflows. Start with the files you use most frequently, then work through your archives at a sustainable pace. Every DOC file converted to DOCX is a small step toward a cleaner, more maintainable document ecosystem.