In which folder should the flightplans (company routes) be placed? I have them in I:\Lockheed Martin\Prepar3D v4\Captain_Sim\757-III\routes. Is this correct? But in the FMC I see all the routes from the documents folder.

If you created the route/flight plan using the default P3D4 Flight Planner, you save to the Documents\Prepar3D v4 Files folder.

If you created the route/flight plan with the 757 CDU/FMC (usually referred to as the CDU), then you save it from the CDU (after activating the route/flight plan), and it will be saved in the I:\Lockheed Martin\Prepar3D v4\Captain_Sim\757-III\routes folder as a Captain Sim .rt file, that can only be loaded using the 757 CDU.

Thanks for your quick response. I use the flightplans made with Simbrief. So these are not usable?

Save them to Documents\Prepar3D v4 Files folder, load them using the CDU > RTE 1 > Send > Fltsim Fpls > Select the saved route from the list (you just scroll through the pages (PREV PAGE/NEXT PAGE buttons) until you find it).

OK. That's the way I use to do it now.

Question...in my routes folder there are no routes in there, but when I go into the FMC, they are there.  I have done a lot of flights in the 757/767 and have quite a few routes I would like to delete..where can I find them at...

Thanks!

Are the routes you see listed under CO RTES or FLTSIM FPLS? If they are under FLTSIM FPLS then they are the saved routes from the Documents\Prepar3D v4 Files (Documents\Prepar3D v5 Files, or Flight Simulator X Files) folder made using the default Flight Planner for the sim (FSX/SE/P3D4/P3D5).
Those listed under CO RTES are the ones saved using the 757 Captain III CDU