BookStack/app/Config/dompdf.php

<?php

/**
 * DOMPDF configuration options.
 *
 * Changes to these config files are not supported by BookStack and may break upon updates.
 * Configuration should be altered via the `.env` file or environment variables.
 * Do not edit this file unless you're happy to maintain any changes yourself.
 */
$dompdfPaperSizeMap = [
    'a4'     => 'a4',
    'letter' => 'letter',
];

return [

    'show_warnings' => false,   // Throw an Exception on warnings from dompdf
    'orientation'   => 'portrait',
    'defines'       => [
        /**
         * The location of the DOMPDF font directory.
         *
         * The location of the directory where DOMPDF will store fonts and font metrics
         * Note: This directory must exist and be writable by the webserver process.
         * *Please note the trailing slash.*
         *
         * Notes regarding fonts:
         * Additional .afm font metrics can be added by executing load_font.php from command line.
         *
         * Only the original "Base 14 fonts" are present on all pdf viewers. Additional fonts must
         * be embedded in the pdf file or the PDF may not display correctly. This can significantly
         * increase file size unless font subsetting is enabled. Before embedding a font please
         * review your rights under the font license.
         *
         * Any font specification in the source HTML is translated to the closest font available
         * in the font directory.
         *
         * The pdf standard "Base 14 fonts" are:
         * Courier, Courier-Bold, Courier-BoldOblique, Courier-Oblique,
         * Helvetica, Helvetica-Bold, Helvetica-BoldOblique, Helvetica-Oblique,
         * Times-Roman, Times-Bold, Times-BoldItalic, Times-Italic,
         * Symbol, ZapfDingbats.
         */
        'font_dir' => storage_path('fonts/'),  // advised by dompdf (https://github.com/dompdf/dompdf/pull/782)

        /**
         * The location of the DOMPDF font cache directory.
         *
         * This directory contains the cached font metrics for the fonts used by DOMPDF.
         * This directory can be the same as DOMPDF_FONT_DIR
         *
         * Note: This directory must exist and be writable by the webserver process.
         */
        'font_cache' => storage_path('fonts/'),

        /**
         * The location of a temporary directory.
         *
         * The directory specified must be writeable by the webserver process.
         * The temporary directory is required to download remote images and when
         * using the PFDLib back end.
         */
        'temp_dir' => sys_get_temp_dir(),

        /**
         * ==== IMPORTANT ====.
         *
         * dompdf's "chroot": Prevents dompdf from accessing system files or other
         * files on the webserver.  All local files opened by dompdf must be in a
         * subdirectory of this directory.  DO NOT set it to '/' since this could
         * allow an attacker to use dompdf to read any files on the server.  This
         * should be an absolute path.
         * This is only checked on command line call by dompdf.php, but not by
         * direct class use like:
         * $dompdf = new DOMPDF();  $dompdf->load_html($htmldata); $dompdf->render(); $pdfdata = $dompdf->output();
         */
        'chroot' => realpath(public_path()),

        /**
         * Whether to use Unicode fonts or not.
         *
         * When set to true the PDF backend must be set to "CPDF" and fonts must be
         * loaded via load_font.php.
         *
         * When enabled, dompdf can support all Unicode glyphs. Any glyphs used in a
         * document must be present in your fonts, however.
         */
        'unicode_enabled' => true,

        /**
         * Whether to enable font subsetting or not.
         */
        'enable_fontsubsetting' => false,

        /**
         * The PDF rendering backend to use.
         *
         * Valid settings are 'PDFLib', 'CPDF' (the bundled R&OS PDF class), 'GD' and
         * 'auto'. 'auto' will look for PDFLib and use it if found, or if not it will
         * fall back on CPDF. 'GD' renders PDFs to graphic files. {@link * Canvas_Factory} ultimately determines which rendering class to instantiate
         * based on this setting.
         *
         * Both PDFLib & CPDF rendering backends provide sufficient rendering
         * capabilities for dompdf, however additional features (e.g. object,
         * image and font support, etc.) differ between backends.  Please see
         * {@link PDFLib_Adapter} for more information on the PDFLib backend
         * and {@link CPDF_Adapter} and lib/class.pdf.php for more information
         * on CPDF. Also see the documentation for each backend at the links
         * below.
         *
         * The GD rendering backend is a little different than PDFLib and
         * CPDF. Several features of CPDF and PDFLib are not supported or do
         * not make any sense when creating image files.  For example,
         * multiple pages are not supported, nor are PDF 'objects'.  Have a
         * look at {@link GD_Adapter} for more information.  GD support is
         * experimental, so use it at your own risk.
         *
         * @link http://www.pdflib.com
         * @link http://www.ros.co.nz/pdf
         * @link http://www.php.net/image
         */
        'pdf_backend' => 'CPDF',

        /**
         * PDFlib license key.
         *
         * If you are using a licensed, commercial version of PDFlib, specify
         * your license key here.  If you are using PDFlib-Lite or are evaluating
         * the commercial version of PDFlib, comment out this setting.
         *
         * @link http://www.pdflib.com
         *
         * If pdflib present in web server and auto or selected explicitely above,
         * a real license code must exist!
         */
        //"DOMPDF_PDFLIB_LICENSE" => "your license key here",

        /**
         * html target media view which should be rendered into pdf.
         * List of types and parsing rules for future extensions:
         * http://www.w3.org/TR/REC-html40/types.html
         *   screen, tty, tv, projection, handheld, print, braille, aural, all
         * Note: aural is deprecated in CSS 2.1 because it is replaced by speech in CSS 3.
         * Note, even though the generated pdf file is intended for print output,
         * the desired content might be different (e.g. screen or projection view of html file).
         * Therefore allow specification of content here.
         */
        'default_media_type' => 'print',

        /**
         * The default paper size.
         *
         * North America standard is "letter"; other countries generally "a4"
         *
         * @see CPDF_Adapter::PAPER_SIZES for valid sizes ('letter', 'legal', 'A4', etc.)
         */
        'default_paper_size' => $dompdfPaperSizeMap[env('EXPORT_PAGE_SIZE', 'a4')] ?? 'a4',

        /**
         * The default font family.
         *
         * Used if no suitable fonts can be found. This must exist in the font folder.
         *
         * @var string
         */
        'default_font' => 'dejavu sans',

        /**
         * Image DPI setting.
         *
         * This setting determines the default DPI setting for images and fonts.  The
         * DPI may be overridden for inline images by explictly setting the
         * image's width & height style attributes (i.e. if the image's native
         * width is 600 pixels and you specify the image's width as 72 points,
         * the image will have a DPI of 600 in the rendered PDF.  The DPI of
         * background images can not be overridden and is controlled entirely
         * via this parameter.
         *
         * For the purposes of DOMPDF, pixels per inch (PPI) = dots per inch (DPI).
         * If a size in html is given as px (or without unit as image size),
         * this tells the corresponding size in pt.
         * This adjusts the relative sizes to be similar to the rendering of the
         * html page in a reference browser.
         *
         * In pdf, always 1 pt = 1/72 inch
         *
         * Rendering resolution of various browsers in px per inch:
         * Windows Firefox and Internet Explorer:
         *   SystemControl->Display properties->FontResolution: Default:96, largefonts:120, custom:?
         * Linux Firefox:
         *   about:config *resolution: Default:96
         *   (xorg screen dimension in mm and Desktop font dpi settings are ignored)
         *
         * Take care about extra font/image zoom factor of browser.
         *
         * In images, <img> size in pixel attribute, img css style, are overriding
         * the real image dimension in px for rendering.
         *
         * @var int
         */
        'dpi' => 96,

        /**
         * Enable inline PHP.
         *
         * If this setting is set to true then DOMPDF will automatically evaluate
         * inline PHP contained within <script type="text/php"> ... </script> tags.
         *
         * Enabling this for documents you do not trust (e.g. arbitrary remote html
         * pages) is a security risk.  Set this option to false if you wish to process
         * untrusted documents.
         *
         * @var bool
         */
        'enable_php' => false,

        /**
         * Enable inline Javascript.
         *
         * If this setting is set to true then DOMPDF will automatically insert
         * JavaScript code contained within <script type="text/javascript"> ... </script> tags.
         *
         * @var bool
         */
        'enable_javascript' => false,

        /**
         * Enable remote file access.
         *
         * If this setting is set to true, DOMPDF will access remote sites for
         * images and CSS files as required.
         * This is required for part of test case www/test/image_variants.html through www/examples.php
         *
         * Attention!
         * This can be a security risk, in particular in combination with DOMPDF_ENABLE_PHP and
         * allowing remote access to dompdf.php or on allowing remote html code to be passed to
         * $dompdf = new DOMPDF(, $dompdf->load_html(...,
         * This allows anonymous users to download legally doubtful internet content which on
         * tracing back appears to being downloaded by your server, or allows malicious php code
         * in remote html pages to be executed by your server with your account privileges.
         *
         * @var bool
         */
        'enable_remote' => env('ALLOW_UNTRUSTED_SERVER_FETCHING', false),

        /**
         * A ratio applied to the fonts height to be more like browsers' line height.
         */
        'font_height_ratio' => 1.1,

        /**
         * Enable CSS float.
         *
         * Allows people to disabled CSS float support
         *
         * @var bool
         */
        'enable_css_float' => true,

        /**
         * Use the more-than-experimental HTML5 Lib parser.
         */
        'enable_html5parser' => true,

    ],

];