Welcome between the users of TeX.SE. What is, please, the full code that gives you this error?
– SebastianoNov 12 '19 at 20:38
7
Remove the space in the command: \begin{document}. This isn't guaranteed to be the problem, but it's an obvious thing to fix. Spaces in environment names aren't a good idea.
– barbara beetonNov 12 '19 at 20:45
\begin{document}. This isn't guaranteed to be the problem, but it's an obvious thing to fix. Spaces in environment names aren't a good idea. – barbara beeton Nov 12 '19 at 20:45