# Make "Appendix" its own part once & its own bookmark

I would like my "Appendices" section to appear as its own part (my book is structured around Parts, Chapters, Sections, etc.) in the TOC and in the PDF bookmarks.

My issue has already been tackled, here and here. I went with the second solution suggested on this page. It works ... but not quite, as you can see in the screen capture I've included under this note: "Appendices" appears as its own bookmark (good), but there are now two entries saying "Appendices" pointing to the same page (bad) -- similarly, when you run the code (included below), you also obtain two TOC entries for "Appendices" (bad).

I would like a single page stating "Appendices" (like the book's "Parts" appear, and then, on the following page, the first Appendix entry, which in the example below is the entry "Lyrics".

Note: although the code I've included below doesn't show it, I use the \input{Appendix} command to access the text my Appendix contains.

Thanks for you help.

% PREAMBLE %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\documentclass[oneside,centered,twocolumn]{book}
%\usepackage[T1]{fontenc}
\special{papersize=215.9mm,279.4mm}
\usepackage[english]{babel}

\usepackage[sc]{mathpazo}
\usepackage{tocloft} % Customization of TOC LOF LOT
\usepackage[toc,page]{appendix}
\usepackage{colortbl} % To define colors
\usepackage{multirow}
\usepackage{eso-pic}
\usepackage{epigraph}
\usepackage{caption} % To change the way captions are labelled
\usepackage{pdfpages}
\usepackage{ltablex}
\usepackage{nicefrac} % to write fractions
\usepackage{attrib} % For source of quotations
\usepackage{lettrine} % For NewThought formatting
\usepackage{array} % To define width of columns in long table
\usepackage{booktabs} % Nicer spacing in columns
\usepackage{siunitx} % To write Celsius, etc.
\usepackage{enumitem} % To create item lists
\usepackage[rightmargin=0pt]{quoting}
\usepackage{scrextend}
\usepackage{threeparttable} % For table notes + To allow footnote material to stay with the tabular environment
\usepackage{relsize,etoolbox} % To make table footnote font smaller and quotes small
\usepackage{threeparttablex}
\appto\TPTnoteSettings{\footnotesize}
\usepackage{textcomp} % For Numero symbol
\usepackage{titlesec}
\usepackage[linguistics,edges]{forest}
\usepackage{tikz}
\usetikzlibrary{calc}
\usepackage{titling}
\usepackage{fancyhdr}
\usepackage{fontspec}

\setmainfont{TeX Gyre Pagella} % Palatino clone

\usepackage{bookmark}

% HEADING and PART FONTS %%%%%%%%%%%%%%%%%%%%%%%%

\newfontfamily\partfont[]{Candara}

% STYLE PART WITH GRAPHICS AND WORK STYLE %%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\titleformat{\part}[display]
{\bfseries\color{black}\filcenter\fontsize{60}{70}\partfont} % Size of Part
{\thispagestyle{empty}\Huge\MakeUppercase\partfont\thepart} % <=========
{10pt}
{\tikz[remember picture,overlay]\node[inner sep=0pt] at ($(current page.north) + (0pt,-400pt)$) {\includegraphics{example-image-duck}};%
}

% STYLE CHAPTER PAGE WITH GRAPHICS AND WORK STYLE %%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\titleformat{\chapter}[display]
{12pt}
{\tikz[remember picture,overlay]\node[inner sep=0pt] at ($(current page.north) + (0pt,-117pt)$) {\includegraphics[width=14cm]{example-image-a}};}
\titlespacing{\chapter}{0pt}{50mm}{42.5mm}

% WATERMARK ADDITIONS FOR BACKGROUND IMAGE BEHIND APPENDICES %%%%%%%%%%%%%%%%%%%%%%

\usepackage[printwatermark]{xwatermark}
\newwatermark[pages=595-595]{\includegraphics{example-image-duck}}

\newlength{\drop}

\begin{document}

\frontmatter
\tableofcontents

\part{Fish}

\chapter{Fortification}
\chapter{Whales}

\bookmarksetupnext{level=-1}
\appendix
\appendixpage

\chapter{Lyrics}
\section{Whales}
\subsubsection{Dogs}
\chapter{Cats}
\chapter{Dice}

\end{document}


I tried your MWE with pdflatex only to be told that as you had used fontspec I had to use either xelatex (which gave a segmentation fault) or lualatex which couldn't find a font you had used. I wasn't a happy camper.
In your document don't use \addappheadtotoc, just the \appendixpage and you will get what I think you want. GOM