\documentclass[11pt,a4paper]{article}
\usepackage{parskip}
\usepackage{ragged2e}
\usepackage{fontspec,polyglossia,url,setspace}
\usepackage[left=1.5in, right=1in, top=1in, bottom=1in]{geometry}
\setmainfont{Pyidaungsu-2.5.3_Regular.ttf}
\begin{document}
\doublespacing
%\onehalfspacing
\input{01_LetterNum}
\input{02_To}
\input{03_Subject}
\input{04_Body}
\\
\\
\input{05_Sig}
\input{06_CC}
\end{document}