# Strange error with inputenc [closed]

The head of my document looks like

\documentclass[intlimits,twoside,a4paper]{article}

\usepackage[utf8]{inputenc}
\usepackage[eqsecnum]{cmpj3}
\usepackage{bm}

\usepackage{float}

\newcommand{\ii}{\mathrm{i}}

\articletype{Regular article}


But when I try to compile the document, it fails and writes:

Package inputenc Error: Keyboard character used is undefined(inputenc) in inputencoding utf8. \section.

The error appears for the string \section{Derivation}, but I don't understand, what is the reason for this.

Can you help?

• inputenc defines definitions for a few hundred characters and Unicode has a few thousand characters so getting this error is expected. If you had shown the full error, or shown a test document, we would know which character was undefined, and could suggest a definition. – David Carlisle Jul 19 '17 at 6:51