Your organization is moving to Microsoft 365. IT has already started rolling it out. And somewhere in the back of your mind, you're wondering about the .xls workbooks with 12 years of macros, the .mdb databases running the department's inventory system, the Excel reports that run automatically every Monday morning.
The question most people don't ask until it's too late: will those files still work in Office 365?
The answer depends on what exactly is in your files — and which part of "Office 365" you're actually talking about.
This is where most of the confusion starts. "Office 365" (now called Microsoft 365) refers to both a subscription plan and a set of apps. But there are two fundamentally different versions of those apps:
For legacy file compatibility, these two behave very differently. The desktop apps are largely backwards-compatible with legacy formats. The web apps are not.
The Office 365 Excel desktop app opens .xls and .xlsm files, but with some important differences from older versions:
| Feature | Office 2010/2013 | Office 365 Desktop |
|---|---|---|
| .xls files | Opens natively | Opens in compatibility mode |
| VBA macros | Runs with warning | Blocked by default for files from email/internet |
| ActiveX controls | Generally works | Some 32-bit controls fail on 64-bit Office |
| Win32 API calls (Declare) | Works on 32-bit Office | Requires PtrSafe keyword for 64-bit |
| Trusted Locations | Configured per-machine | Same, but Group Policy may override |
The most significant practical change: macro security defaults are stricter in Office 365. Files that weren't in a Trusted Location in older Office might have prompted "Enable Content" and run. In newer Office 365 versions (post-2022), files from network shares or email attachments may be blocked entirely without a manual unblock step.
If your users are emailing .xls macro files to each other, those files will increasingly be stopped at the door.
Here the story is more stark. Access is only included in Microsoft 365 Business Standard, Business Premium, and Enterprise plans — not personal or family plans.
More importantly: modern Access has limited .mdb support. Access 2013+ can still open and edit existing .mdb files, but cannot create new ones. Some legacy features are unavailable in .mdb files opened in modern Access:
If any users start opening legacy files via browser — SharePoint, OneDrive, or the Office 365 web interface — the compatibility story collapses entirely.
Excel Online does not support VBA macros. A file opened in Excel Online will display the data but all macro functionality is silently disabled. Users who click a button and nothing happens won't necessarily know why.
Excel Online does not fully support ActiveX controls. Embedded controls render as static elements or disappear.
Access has no web equivalent in Microsoft 365. The old Access Web Apps feature was discontinued in 2017. There is no browser-based Access app in the current Microsoft 365 suite.
The implication: any workflow that relies on users being able to open legacy Office files from SharePoint or OneDrive in the browser will break unless those files are migrated to modern formats first.
Office 365 defaults to 64-bit installation. Most older desktop Office versions were 32-bit. This creates a specific problem for legacy files:
Declare Function or Declare Sub to call Windows DLLs needs the PtrSafe keyword for 64-bit Office. Without it, the macro won't compile.LegacyLeaps scans your .xls and .mdb files and tells you exactly what VBA code, ActiveX controls, and API declarations are present — before you upgrade Office.
Try the Free ScanTo be fair: most of what's in a typical legacy .xls or .mdb file survives an Office 365 migration without any intervention:
The files that need attention are the ones with complex VBA, Win32 API calls, or 32-bit ActiveX dependencies. Those are a specific subset — but an important one, because they tend to be the most business-critical files.
Before rolling out Office 365 to users with legacy files:
For a complete audit guide, see How to Audit Your Organization for Legacy File Risk.
Office 365 desktop apps are largely backwards-compatible with legacy formats — but with stricter security defaults, a 64-bit runtime that breaks old API calls and ActiveX controls, and no .mdb support in modern Access.
The web apps are a clean break: no VBA, no macros, no .mdb.
If your organization has legacy Office files in active use, the time to address them is before the Office 365 rollout, not during or after. A pre-migration scan reveals exactly what needs attention — in most cases, the files that will actually break are a small fraction of the total library.
Scan your legacy files before the rollout. LegacyLeaps identifies every macro, ActiveX control, and API declaration — and converts the files that need it. 100% Money-Back Guarantee: if it doesn't preserve your formulas, macros, and formatting, we'll refund every penny.
Download Free ScannerRelated: Windows Upgrade Survival Guide for Office Files · What Happens to .xls Files in Office 365
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