The Simple Way to Convert a Line to a Shape in Illustrator
The day I found this function I was genuinely happy. It is great for outlining dotted lines, making interesting shapes, creating rounded corner triangles and combining strokes with shapes.
1. Select your line or stroke
2. OBJECT > PATH > OUTLINE STROKE
3. Use the UNITE (1st option) in your Pathfinder to combine the shapes if required. Easy!
*This also works when you have a stroke on an object.