I am using a \usepackage{txfonts} because of this symbol \multimapdotbothB but the body text or fonts are affected. How can this be not to be affected?
\documentclass{article}
\usepackage{lipsum}
\usepackage{txfonts}
\begin{document}
\lipsum[1]
$\multimapdotbothB$
\end{document}
Just load the single symbol:
\documentclass{article}
\usepackage{lipsum}
%\DeclareSymbolFont{symbolsC}{U}{txsyc}{m}{n}
%\SetSymbolFont{symbolsC}{bold}{U}{txsyc}{bx}{n}
\DeclareSymbolFont{symbolsC}{U}{ntxsyc}{m}{n}
\SetSymbolFont{symbolsC}{bold}{U}{ntxsyc}{b}{n}
\DeclareMathSymbol{\multimapdotbothB}{\mathrel}{symbolsC}{24}
\begin{document}
\lipsum[1]
$\multimapdotbothB$
\end{document}
I've loaded the newtxmath font, which is based on txfonts. I added the two commented lines in case you have an old TeX distribution.
