documentclass{minimal}
usepackage{graphicx}
usepackage{titleps}

newpagestyle{mystyle}{
    setfoot{}{}{includegraphics[width=30mm]{logo}}
}
pagestyle{mystyle}

begin{document}

Test.

end{document}

This is pdfTeX, Version 3.14159265-2.6-1.40.18 (TeX Live 2017) (preloaded format=pdflatex)
 restricted write18 enabled.
entering extended mode
(./mwe.tex
LaTeX2e <2017-04-15>
Babel <3.10> and hyphenation patterns for 84 language(s) loaded.
(/usr/local/texlive/2017/texmf-dist/tex/latex/base/minimal.cls
Document Class: minimal 2001/05/25 Standard LaTeX minimal class
) (/usr/local/texlive/2017/texmf-dist/tex/latex/graphics/graphicx.sty
(/usr/local/texlive/2017/texmf-dist/tex/latex/graphics/keyval.sty)
(/usr/local/texlive/2017/texmf-dist/tex/latex/graphics/graphics.sty
(/usr/local/texlive/2017/texmf-dist/tex/latex/graphics/trig.sty)
(/usr/local/texlive/2017/texmf-dist/tex/latex/graphics-cfg/graphics.cfg)
(/usr/local/texlive/2017/texmf-dist/tex/latex/graphics-def/pdftex.def
(/usr/local/texlive/2017/texmf-dist/tex/generic/oberdiek/infwarerr.sty)
(/usr/local/texlive/2017/texmf-dist/tex/generic/oberdiek/ltxcmds.sty))))
(/usr/local/texlive/2017/texmf-dist/tex/latex/titlesec/titleps.sty
(/usr/local/texlive/2017/texmf-dist/tex/latex/titlesec/ttlps.def))

! LaTeX Error: Missing begin{document}.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
 ...

l.8 pagestyle{mystyle}

?

setfoot{}{includegraphics[width=30mm]{logo}}{}