Unwanted lines in door openings

[Wagurto]

I need to get rid of this lines (see attached image)

[PeterJ]

Could they be the edge of a floor? Or are the doors inserted for some reason just a touch above the floor level?

[Allen Lacy]

What you're seeing is the edge of the floors. I usually use the linework tool and make the edges invisible lines.

[David]

By adjusting the bottom range of your view an inch or so above the floor level, you will not see the floor line. A good option if walls cover the floor except at door openings.