The example in the question has two documentclass commands, which is not allowed in LaTeX. You can use a single command with the convert option added to the options of the first line.
Note that the second 2pt option does not do anything, it generates a warning and it can be removed. Note also th...
@MathWizard the log file is created in the same folder as the pdf. It has the same name as the .tex and .pdf files but then with a .log extension (e.g., in my example above the source is called convpng.tex, the pdf is called convpng.pdf and the log file is called convpng.log). You can open the log file in any text editor, for example Notepad in Windows. It should have some lines containing the word runsystem and convert. If there are errors they will be reported around those lines.
it's not the short example I put in my answer but let's see if we can find something
it says (line 80 and a bit above): Class standalone Warning: Conversion failed! Please ensure that shell escape (standalone) is enabled (e.g. use '-shell-escape').
but, as I explained in my answer, if you put at the top of your file the line % !TeX TXS-program:compile = txs:///pdflatex/[--shell-escape] then it might work
if that doesn't work there are some other solutions
with the %, so the first line of your file should be:
Discussion between Marijn and Math Wi…
Discussion between Marijn and Math Wi…