Licensing is a thorny issue. Office follows the Universal License Terms [0] which have various restrictions, such as not offering Office to 3rd parties and all

Licensing is a thorny issue. Office follows the Universal License Terms [0] which have various restrictions, such as not offering Office to 3rd parties and all users internal to a company who use a service like yours would require an Office CAL themselves. You would need a Volume License subscription for Office client. Retail copies are most definitely not licensed for this use-case. This would include anyone using your software -- they would need to have a volume licensed copy of Office. I would suggest talking to a company like CDW who can assist with license terms or Microsoft Licensing -- don't take an HN or any other forum reply as a definitive answer. Microsoft typically doesn't let you get away 'cheap' when you use their software like this. And they've covered all of the bases you can think of to be cheap. Since docx is 'open', any masochistic third party can write a library to interact with it -- or just take from the likes of LibreOffice and adapt it for server-side software. This avoids the Microsoft licensing discussion. [0] https://www.microsoft.com/licensing/terms/product/ForallSoftware/all https://www.microsoft.com/licensing/terms/product/ForallSoft...