# Trigger a newgeometry starting at a certain page

I'm trying to make letters without relying on predefined classes to that effect (why not?). In the example below, I'd like the top margin to be changed to 0.75in after page 1.

\documentclass[12pt]{report}
\usepackage[english]{babel}
\usepackage{datetime}
\usepackage[
% https://css.paperplaza.net/conferences/support/page.php
letterpaper,
top=1in, %first
% top-0.75in,%rest
left=0.75in,
right=0.75in,
bottom=0.75in,
showframe%only for testing
]{geometry}
\usepackage{lipsum}
\usepackage{titleps}
\usepackage{xparse}

{O{}+mO{\newline}}
{\noindent #1#2#3}

\newpagestyle{rest}
[\small\sffamily]
{
\setfoot{}{\thepage}{}

% this has no effect
%  \newgeometry{%
%    letterpaper,
%    % top=1in, %first
%    top=0.75in,%rest
%    left=0.75in,
%    right=0.75in,
%    bottom=0.75in
%  }

}

\begin{document}
\thispagestyle{empty}
\pagestyle{rest}

1000 Main Street\\
Washington, DC}

1001 Main Street\\
Washington, DC}

\lipsum[1-5]\\

\vspace*{3em}

\end{document}


Set your page margins according to the requirements for the bulk of your document. In your case, this would be

\usepackage[
% https://css.paperplaza.net/conferences/support/page.php
letterpaper,
margin = 0.75in
]{geometry}


Then, issue \vspace*{0.25in} on the first page (or, \AtBeginDocument{\vspace*{0.25in}} in the preamble) which reduces the text block on the first page by 1/4in (or, increases the top margin by 1/4in).

Here is a template showing the use-case:

\documentclass{article}

\usepackage[
margin = 0.75in,
showframe% Just for this example
]{geometry}
\usepackage{lipsum}

\AtBeginDocument{\vspace*{0.25in}}

\begin{document}

\sloppy% Just for this example
\lipsum[1-15]

\end{document}


Your document will have the same margins for all pages, even with the change on the first page (visualised by adding the showframe option to you geometry settings).

The flowfram package is a bit wasted on something this simple. But changing the geometry of specific pages is precisely what it does.

\documentclass[12pt]{report}
\usepackage[english]{babel}
\usepackage{datetime}
\usepackage[
% https://css.paperplaza.net/conferences/support/page.php
letterpaper,
top=0.75in,% use larger
left=0.75in,
right=0.75in,
bottom=0.75in,
showframe%only for testing
]{geometry}
\usepackage{lipsum}
\usepackage{titleps}
\usepackage{xparse}

\usepackage{flowfram}
\newflowframe[1]{\textwidth}{\dimexpr \textheight-.25in}{0pt}{0pt}

{O{}+mO{\newline}}
{\noindent #1#2#3}

\newpagestyle{rest}
[\small\sffamily]
{
\setfoot{}{\thepage}{}

% this has no effect
%  \newgeometry{%
%    letterpaper,
%    % top=1in, %first
%    top=0.75in,%rest
%    left=0.75in,
%    right=0.75in,
%    bottom=0.75in
%  }

}

\begin{document}
\thispagestyle{empty}
\pagestyle{rest}

1000 Main Street\\
Washington, DC}

1001 Main Street\\
Washington, DC}

\lipsum[1-5]\\

\vspace*{3em}