With all the wainscotting going on you have to remove existing trim around the opening, pack the opening out the opening for a new door, drywall, etc install new door trim to match the existing, and match wainscotting on both sides of the opening.

Here is an example to give you an idea.

What he said, basically you will be stripping the wall and reframe or packing in the opening smaller to accommodate the door. New drywall, and trim will be required..

I've done several similar to this, filling in the opening without removing trim.

Nice, I’m not sure you can see the detail of the trim. It’s on the ouside, inner and wraps around to inside. Also, is that door for interior or exteriorer? were they custom made?

I don't see a problem with the trim. The doors I've used were stock interior wood doors.

Here is another option, using 3 equal sized panels. With a 101w x 96h opening, 3, 3'x8' doors could be used. You would need to work with your supplier on availability.

You will need a good carpenter to put everything together on site, or find a door shop to supply the parts.