Word Version Incompatibility

There is generally no inherent incompatibility between the Word desktop app in Microsoft 365 Personal and the Word app in Office/Word 2021 Business. Both can open and edit old Word 97–2003 .doc files, and Microsoft’s compatibility mode is specifically meant to support older documents.

What you’re seeing is more likely a problem with that specific .doc file, your Word installation, or how Word is handling compatibility mode, not a fundamental mismatch between the two product versions. Microsoft notes that Word 2021 can open Word 97–2003 documents, and in cases like the “not enough memory or disk space” message, a repair of Office is often suggested.

What tyou can try…

• Open the .doc file in Word and use File > Info > Check for Issues > Inspect Document or Compatibility Checker. Word’s compatibility tools can reveal old-format features and conversion issues.
• Save a copy as .docx and work from that version going forward. That usually avoids legacy-format problems.
• Repair the Office/Word installation if the same .doc file keeps triggering the error. Microsoft’s guidance for this kind of issue commonly points to a repair.
• If possible, open the file on another machine or in another Word installation to check whether the file itself is the cause.

Practical conclusion…

Your two Word versions are not the main issue here. The fact that the file behaves normally when saved as .docx strongly suggests the problem is tied to the old .doc format, not to Microsoft 365 Personal versus Office 2021 Business.

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