Using the Boolean Modifier as @John Eason said in his comment, you could use a mesh plane rotated and located as needed for the cutter.
I have made an object similar to the image showing Fig 11i. Note that the axes I use may differ from your object's orientation.
Add a mesh plane, Using Global Transformation Orientation rotate it on the X axis 45 degrees:
Then rotate the plane on the Y axis 45 degrees. Press Ctrl->A and apply rotation:
Move the plane on the Y axis to the location required:
With the object selected add a Boolean Modifier. Either click in the Object box and select the plane, or use the eyedropper and click it on the plane in the viewport. Select the Fast option:
Result after applying the Modifier: