I have a PDF (exported from CAD) that I am working with in Illustrator CS5. Lines in the PDF are made of triangles, and I would like to convert the lines to be a single stroked path. What is the best way to do that using Illustrator?
You can't convert a series of shapes to a single stroked path. At least not reliably with any automated method. And any manual method would take some effort - such as combining the shapes to a single shape, deleting the end cap paths, then blending between the outer paths, expanding the blend, then removing the outer (original paths) leaving one center path which could be then stroked.
You can select the shapes and use
Pathfinder > Merge or
Pathfinder > Unite to create a single shape.
However, if you want a stroked path the best solution is most often to redraw the path yourself and delete the original shapes.