Instruction: Extract information from the supporting document to answer the given question.

Input:
Question: I just bought the canon 1.4 EF extender III to attach it to my Super telephoto 400mm 5.6f  . Will the Autofocus work on my Canon 7D Mark II?
Document: Second EF telephoto extender purchased. First was a Canon EF 2.0X III which worked great on my 70-200mm f/2.8L IS II USM. Then purchased 500mm f/4L IS II USM on which the 2.0X III would not work (autofocus issue) so purchased the 1.4X III. Autofocus not a problem with the 1.4X III on the 500mm. Both teleconverters produced clear sharp images.
I use this 1.4X III Telephoto Extender with my Canon EF 70-200 mm f/2.8 L and Canon EF 100-400 mm f/4.5-5.6L IS USM telephoto zoom lenses and am very happy with the results. Plus the small size and light weight makes it easy to bring along in your bag just in case you need a little extra reach. Highly recommended.
With the Canon EF 1.4X III you can extend your lens focal length and still have fantastic picture quality for much less than buying a new lens.NOTE:  The auto focus compatibility is a little confusing. Canon states that auto focus will work if your lens max lens aperture is 5.6 or faster. I also verified that Canon states that this extender is compatible with the Canon EF 100-400 f/4.5-5.6 lens.
I recently purchased this for a Canon 7D, with a EF 400 mm / 5.6 lens for bird photography. Mainly for raptors on cliffs, instead of birds in flight. I am pleased with the combination, giving a 560 mm focal length. My autofocus does not work, as expected, with the extender. That is ok though as it is bright enough in the viewfinder for manual focus.
The extender is easy to use and worked very well with my Canon 400mm f/2.8L IS II USM giving me 560mm f/4. I must point out that autofocus speed does reduce with the TC. At f/2.8 the lens is super fast, and the TC causes autofocus to be affected  -- if you are looking for fast action, this can play a role.
I received the Canon ext 1.4 III on time and couldn't wait to test it out. I'd like to state I did have the ext II, never happy with the results. But this one, the ext III is truly awesome. I just bought the Canon 300mm f4 IS USM. When I coupled this lens with the ext III on my canon 1D Mk IV, and 5D Mk II I was blown away with the results. You will not be disappointed with the ext 1.4 III.
It's a great teleconvertor but please review whether it is compatible with the lenses you have. Autofocus did not work for me for a Canon 40D body and 70-200m/4L and 100-400mm/4-5.6L lenses.
I was also hoping that this extender would work with my Sigma 150-500mm lens. It will not fit, this extender only works with certain Canon Lens (I believe only with L series lens -- see below). I kind of wish I had just bought the Kenko 1.4x teleconverter instead now, since I wanted the option to use the extender with the Sigma lens.----- !! -------Updated review. 3/5/2102.
I'm a professional photographer and using this to give me some extra power on my Canon EF 300mm 2.8 lens for outdoor game photography. I often shoot from a standard sized football/soccer field from the end zone and can capture clear full-body sized action images when the players are in motion and from about 50 yards can capture good quality upper body/torso shots using the combination 1.4 extender with a 300mm 2.8 telephoto lens.
I purchased the Telephoto converter for my EF 100 - 400 zoom lens which I use on a Canon 6D. Turns out Autofocus does NOT work which makes the converter practically useless to me. Once I add the converter to camera, focus mode shifts to M Focus.Reviews I read did not suggest this to be an issue.
Answer: Yes the specs say it will focus at f8