Boolean and Pro - Boolean

Create large flat box.

Create letter from shape text.

Turn the spline into an editable poly.

Extrude the letter so that it is deeper than the box.

Place the letter in the middle of the box so that it intersects it.
Select the box.
Go to create > compound objects > pro - boolean.
Under pick boolean Click start picking Click on letter.

Then under parameters sub - object operations click extract selected.

The final image of the extracted shape.