There was never an official released by Microsoft. Most "portable" versions found online are unofficial, third-party repacks that may carry security risks or stability issues.
Rediscover classic productivity: Microsoft Office 2007 Portable Edition brings your trusted Word, Excel, and PowerPoint tools wherever you are — no install, no cloud, and no fuss. Edit legacy files with confidence, carry your templates and font set on a single USB stick, and work the way you remember: fast, familiar, and distraction-free. microsoft office 2007 portable edition
A genuine licensed copy of Office 2007 also included OneNote, Publisher, and Groove, but portable repacks typically strip these out to save space, often compressing the suite down to 200–400 MB. There was never an official released by Microsoft