I'd go with an Atrium door instead.
The reason why is the threshold is far stronger and I've never once been able to get a Pella or Anderson rep to come look at windows or doors my customers are having trouble with. Home Depot sells Atrium.
I also strongly suggest while the door is out you add what's called a jam sill. It will stop any water from getting in around or under the door and taking out the subfloor.
Pay special attention to the flashing under and around the door for a leak free install.
Make sure the threshold is fully supported on the outside so it can not twist and cause a leak.
A piece of 1 X 6 vinyl lumber attached with SS trim head screws works great.