What's the reason why some TeX files compile fine on TeXworks but others don't?

Question

For example, when I download the ShowcaseCircular.tex file from here, I can see it previewed on the PDF viewer. But when I try pp.tex, I get some kind of error on TeXworks. Why is that?

Answer 1

There are several format to compile the LaTeX code. ShowcaseCircular.tex compiles with pdflatex, while pp.tex compiles with context. You have to choose the appropriate compilation format for the right TeX file.