possibly upload our own .fbx motions into maxiamo?

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I was wondering if it would be possible for us to upload our own .fbx files because the free ones are very limited. Since I use cinema 4d, I do not know of any other way to copy my motions on to a rigged skeleton other than mixamo. This would be extremely helpful because i have downloaded tons of free .fbx but no way to apply to them to my rigged character. If someone knows a easy way of binding movements to a skeleton that does not use mixamo and is free or remotely cheap, please leave an answer. Thanks for your time.