How to straighten a warped door without removing it?

To straighten a warped door without removing it, whether interior wood door or exterior door that is warped due to moisture and temperature changes, you can use moisture, heat, and pressure methods to gradually bring it back to flat while still hung, though severe warps may require removal. First, identify direction of warp by closing door and seeing gap at top or bottom. For wood door warped inward, try tightening hinge screws on warped side to pull door closer to jamb, or add longer 3 inch screws to hinge into stud to pull frame. You can also try applying moisture to concave side and heat to convex side: dampen a towel and place on concave side and apply heat lamp on opposite side to expand wood, though this takes time. For minor warp, place straight 2x4 against warped area and clamp it to door with C-clamps padded with cloth, leaving for 24 to 48 hours to force straight, checking frequently. You can also adjust strike plate position to compensate for warp so door latches. For exterior doors, ensure weatherstripping not causing binding. If warp caused by water damage from leaking gutters above door that cause moisture, fix water source first by cleaning gutters and ensuring downspouts direct water away, as continued moisture will warp again. If door is severely warped more than half inch, it may need to be removed, laid flat with weights for days, or replaced costing 200 to 1000 dollars. Regular sealing and painting prevents warping.