Start from your rigged character and File>Export in FBX 2010.0 format (character in t-pose, default export settings of FBX plugin with Y-up orientation).
Select a Motion Model, Mixamo has thousands of online motions, many more being added each week
Design & Synthesize Motion using built in sliders and controls
Upload your FBX model, automatic mapping for standard rigs
Final Preview & Download, preview to your heart's content, only download when you're satisfied
File>Merge the downloaded FBX file back into Cinema 4D A skeleton (B) identical to the one of your character but with the motion applied will be loaded in the scene. Selecting all joints, press the "key" button to make sure bothe skeletons have at least one keyframe on all curves
Copy motion onto your character skeleton. In the Timeline editor (Show F-Curves) select all the curves of skeleton (B) and copy them. Open the Timeline of character (A) after selecting all joints and paste the curves. At this point you can delete skeleton (B).