Where in France will you be? It's a big country. Are you asking about a few hour walking tour in a city/town or a multi-day walking tour from town to town?
Depends somewhat if you want self-guided (with ample notes and maps supplied), or guided.
For the former, I strongly recommend InnTravel.
Consider also companies that have a local rep. "on the ground" (tend to be a little more expensive):
Headwater.com and BelleFrance.com
Also consider Highpoint Holidays and On Foot Holidays.
For guided look at Kudu, but they don't offer much in France: I tend to use them for countries where I don't speak the language.
For slower pace consider Adagio.
All these are UK-based and prices often include travel from London, but you can always ask for pricing with travel to & from the starting-point not included. Use Rome2rio.com for access from an aiport in France if arriving from the States.
How can anyone answer this question when you are so vague about what you are seeking? A few hours, or multi day tours; guided or self-guided; rugged mountain walks or easy vineyard walks. Too many variables to answer your question.
First time I have ever seen a two-word original post.
You might try walkers world, a subsidiary of Teachers Travel. They do organize walks in France.
I used Paris Walks for a tour of montmarte and was very satisfied.
Backroads offers week long walking tours.
We enjoyed two walking tours with SightSeekers Delight. We choose the Montmarte and Marais tours. We were fortunate to have a small group of 4-6. The guides were knowledgeable and entertaining! We would take future tours with them again.