\documentclass[10pt]{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
%\usepackage[czech]{babel}
\usepackage{a4wide}
\usepackage{tabularx}
\usepackage{graphicx}
\renewcommand{\familydefault}{\sfdefault}
\setlength{\extrarowheight}{3pt}

\begin{document}
\footnotesize

\begin{center}
\begin{tabularx}{\textwidth}{|XXXX|}
\cline{3-4}
\multicolumn{2}{X}{} & \multicolumn{2}{|X|}{} \\
\multicolumn{2}{X}{} & \multicolumn{2}{|l|}{\large Faktura: \hfill {{invoice.number}}} \\
\multicolumn{2}{X}{} & \multicolumn{2}{|X|}{} \\
\hline
& & & \\
\bf Dodavatel: & & \bf Odběratel & \\[1em]
\multicolumn{2}{|l}{\large\bf {{issuer.name}}} & \multicolumn{2}{l|}{\large\bf {{customer.name}}} \\
{{py:
a1 = issuer.address[:]
a2 = customer.address[:]
a1 += (len(a2)-len(a1))*[""]
a2 += (len(a1)-len(a2))*[""]
}}
{{for f1, f2 in zip(a1, a2)}}
\multicolumn{2}{|l}{\large {{f1}}} & \multicolumn{2}{l|}{\large {{f2}}} \\
{{endfor}}

& & & \\
\multicolumn{2}{|l}{IČ: {{issuer.number}}} & \multicolumn{2}{l|}{IČ: {{customer.number}}} \\
& & & \\

{{py:
a1 = issuer.comments[:]
a2 = customer.comments[:]
a1 += (len(a2)-len(a1))*[""]
a2 += (len(a1)-len(a2))*[""]
}}
{{for f1, f2 in zip(a1, a2)}}
\multicolumn{2}{|l}{ {{f1}}} & \multicolumn{2}{l|}{ {{f2}}} \\
{{endfor}}

& & & \\
\hline
& & & \\
\bf Platební podmínky: & & & \\[1em]
\large Forma úhrady: & \large {{"hotově" if invoice.payment=="cash" else "převodem"}} & \large Datum vystavení: & \multicolumn{1}{r|}{\large {{invoice.date.strftime("%d.%m.%Y")}}} \\
\large Číslo účtu: & \large {{issuer.bank_account}} & \multicolumn{2}{l|}{\large\bf Datum splatnosti: \hfill {{invoice.due.strftime("%d.%m.%Y")}}} \\
\large Variabilní symbol: & \large {{invoice.number}} & & \\

{{if invoice.notes}}
& & & \\
\hline
& & & \\
\bf Poznámky: & & & \\[1em]
{{for note in invoice.notes}}
\multicolumn{4}{|l|}{\large {{note}}} \\
{{endfor}}
{{endif}}

& & & \\
\hline
& & & \\
\bf Fakturujeme vám: & & & \\[1em]

{{for item in invoice.items}}
\multicolumn{4}{|l|}{\normalsize {{item[0]}} \hfill {{item[1]}} Kč} \\
{{endfor}}

& & & \\
\hline
& & & \\
\multicolumn{3}{|l}{\large\bf Celkem k úhradě:} & \multicolumn{1}{r|}{\large\bf {{invoice.sum}} Kč} \\
& & & \\
\hline
\multicolumn{4}{r}{} \\
\multicolumn{4}{r}{\includegraphics[scale=1]{../signature.png}\hspace{.4cm} } \\
\end{tabularx}
\end{center}

\end{document}