What Should I Do Before Cutting a Door for an Interlocking Bronze Threshold?

Fit the threshold in the opening before cutting the door.

Classic Door's installation sequence is:

1. Cut and notch the bronze threshold to fit the opening.
2. Dry-fit it at the sill and shim it until it sits level and stable.
3. Put the threshold in its final position and mark where the threshold and J-hook will align.
4. Transfer those marks to the door.
5. Remove the door only after the threshold position has been established.

The door can then be trimmed so it sits about 1/8 inch above the interlocking part of the threshold, and the bottom edge can be prepared for the J-hook.

See the photos and complete sequence in How to Install an Interlocking Bronze Threshold on a Door.