Add content to end of page

Question

is there a simple way to add some content at the end of pages similarly to \AtEndDocument (for example something like \AtThisPageEnd) ?

I looked at everyhook and everypage, but it doesn't look that it's possible to do it with these packages.

Does someone have an idea ?

Edit: To be more precise, I try to change the layout for some page using the geometry package. I manage to make it work when the textwidth is constant. The problem comes when it is not, see this example

\documentclass [a4paper]{article}
\usepackage [showframe]{geometry}
\usepackage {atbegshi}
\usepackage {lipsum}

\title{The Title}
\author{Me}
\date{\today}

\geometry{
    paperwidth=18cm,
    paperheight=18cm,
    textwidth=9cm,
}

\makeatletter

\gdef\setGeometryPage
{
    \ifnum\thepage=2
    \global\let\setGeometryPage =\relax
    \expandafter \@gobble % gobble clearpage
    \newgeometry
    {
        textwidth=12cm,
    }%
    \fi
    \aftergroup\setGeometryPage
}

\AtBeginShipout{

    \AtBeginShipoutUpperLeft{
        \setGeometryPage
    }
}

\makeatother

\begin{document}

\maketitle

\section{First section}

\lipsum[1]
This part is the transition with the next page.
This part is the transition with the next page.
This part is the
%\clearpage\noindent
transition
\lipsum[1-2]

\end{document}

A workaround (not very nice) is to add the \clearpage\noindent at the end of the first page (see example comment). (NB: I'd like to set the layout only with the geometry package here)

Answer 1

What you're looking for is an open problem, so you'll have to resort to some manual intervention. Here are two options:

1. Since you know where the break is located, you can insert a forced paragraph break and ensure that the last line fills the line width. The length at play here is \parfillskip. After that, you can insert your \clearpage\noindent like before:

   \lipsum[1]
   
   {\setlength{\parfillskip}{0pt}% Make last line in paragraph fill the line
   This part is the transition with the next page.
   This part is the transition with the next page.
   This part is the\par%
   }
   
   \clearpage\noindent
   transition
   \lipsum[1-2]
   

2. If you don't want to care about the exact position, but know that you have a certain number of lines before the page break, you can use \parshape to adjust the flow of the paragraph:

   \lipsum[1]
   
   \parshape
     3 % Shape of 3+ lines in the paragraph have to be adjusted
     0pt \linewidth % Line 1 = A regular line (no additional indent, and full \linewidth)
     0pt \linewidth % Line 2 = A regular line (no additional indent, and full \linewidth)
     0pt \dimexpr\linewidth+3cm % Line 3+ = Adjusted (no additional indent, width of \linewidth+3cm)
   This part is the transition with the next page.
   This part is the transition with the next page.
   This part is the
   transition
   \lipsum[1-2]
   

In both instance above, the following output is achieved: