In this article, you will learn how to set custom fonts when converting HTML to PDF. We will cover several conversion tools, including Headless Chrome, WeasyPrint, Prince, wkhtmltopdf and PHP libraries: mPDF, TCPDF and Dompdf.

Some theory about fonts and text

Before we start, there are some terms you should familiarize with.

Most documents are based on text. To build a piece of text you need characters that will make letters and words.

A character set defines mappings between numeric codes and characters: letters, digits, symbols, and so on. For example, in the ASCII table, the decimal number 65 represents a Latin letter A. This is an abstract representation; we still don’t know how this letter should be drawn on screen or printed.

An encoding specifies how the character codes will be represented as bytes. For ANSI this is simple: a byte value 65 (decimal) is equal to ASCII code 65, which represents capital letter A. However, if a character set exceeds 256 possible values of a single byte, we dive into the world of multi-byte encodings. The most popular ones are UTF-8, UTF-16, UTF-32, UCS-2 and UCS-4 for the Unicode standard.

A font is a set of glyphs - readable characters and other symbols that represent a character set. A font data file contains either bitmaps or vectors that make up all the character shapes.

The first thing you need to properly render your HTML code to PDF is a character set declaration:

<html>
  <head>
    <meta charset="utf-8">
  </head>
  <body>
    ...
  </body>
</html>

Having these basics described, we can start using fonts and typing!

Picking a proper font

To use a custom font, first you have to choose one that covers all characters you need in your document or its part. This should be common sense, but sometimes we (or the client) forgets about it.

For example if you pick a fancy header font and your language includes non-Latin characters (accents, umlauts, ogonki, Cyrillic alphabet etc.), check if the font contains glyphs for them! Either use a website that allows testing fonts or download the font files and try them in some text editor or graphics program.

Usually, there are no “one-size-fits-all” solutions. Some fonts do not have an “italic” or “bold italic” versions on purpose. Some fonts contain only uppercase letters (capitals). Other fonts, like fancy handwriting-like ones, are not readable in small sizes.

Font types supported by PDF

The most common font file formats are OpenType, TrueType and Type 1. They differ in features and the way of describing shapes. All of them can be used in a PDF document.

The so-called “web fonts” are usually compressed with a WOFF2 format which is not supported by PDF. Google Fonts, a popular web font provider, fortunately offers a “Download family” feature which gives you the full TrueType archive.

However, if you only have a WOFF2 font file, you can still convert it to TrueType or OpenType. Either use an online tool, or the Linux terminal:

sudo apt install fontforge woff2
woff2_decompress font.woff2

Selecting a font in CSS

Let’s remind ourselves how to pick a font in CSS. The most basic syntax looks like this:

body {
  font-family: Verdana, Arial, sans-serif;
}

The example above means that we prefer the Verdana font, but in case if it’s not available we recommend substituting it either with Arial or any sans-serif font. We depend only on fonts available in a certain system. Every OS has a basic set of fonts, but you can also install your own.

Moreover, every PDF reader provides standard Type 1 fonts, including Times-Roman, Helvetica, Courier and Symbol.

You might want to use a custom font in your document without installing it globally in the operating system. In the example below, we import a font file and assign a local name Lato. We declare this is a normal (not italic) font of a regular weight:

@font-face {
  font-family: 'Lato';
  font-style: normal;
  font-weight: normal;
  src: url('file:///path/to/my/project/lato.ttf') format('truetype');
}

body {
  font-family: Lato;
}

The @font-face syntax works fine with any Chromium-based tools, and also WeasyPrint and Prince. Other tools make selecting a font a bit harder.

Providing a font to wkhtmltopdf

For security reasons, wkhtmltopdf blocks any access to remote font files. It cannot even read a font file from a local drive.

To pick a custom font, we will use a data URL trick. First we have to encode the font file with Base64. We can use either the PHP function base64_encode(), the Linux console command base64 or any Base64 encoder available online.

Then we copy the encoded file contents and paste into the CSS:

@font-face {
  font-family: 'CaslonItalic';
  src: url(data:font/truetype;charset=utf-8;base64,PASTE_IT_HERE) format("truetype");
}

body {
  font-family: CaslonItalic;
}

Because an encoded font file can be very long, it’s more convenient to move the @font-face declaration to a separate CSS file and then use @include to attach it to the main stylesheet. You can decide if you want to include that encoded file in your repository, or generate it on-demand in some build script.

Providing a font to Dompdf

The Dompdf PHP library has its internal font metrics engine which incorporates local caching. The mechanism is cumbersome because you have to manually register the font before using it.

Below, I assume that you’ve installed Dompdf with Composer, hence the vendor directory.

This can be done with a load_font.php script which is available in the dompdf/utils package. Since it would require to copy another repo to the vendor/dompdf/dompdf directory, I don’t really like this method.

Another way is to extend your PDF rendering code. During the first round, Dompdf will create cache files in the vendor/dompdf/dompdf/lib/fonts directory - which means your script must have write access there. Next time, those cached resources will be used to embed the font in a PDF:

use Dompdf\Dompdf;
use Dompdf\Options;

$fontDirectory = '/home/someuser/fonts';

$options = new Options();
$options->setChroot($fontDirectory);

$pdf = new Dompdf($options);
$pdf->getFontMetrics()->registerFont(
    ['family' => 'CaslonItalic', 'style' => 'italic', 'weight' => 'normal'],
    $fontDirectory . '/CaslonItalic.ttf'
);
$pdf->loadHtml($html);
$pdf->render();
file_put_contents('output.pdf', $pdf->output());

The setChroot() call is necessary for security purposes, so that Dompdf won’t access any system files.

Note that when adding a font file you must specify its corresponding style and weight.

Setting a custom font in mPDF

mPDF has a decent documentation which explains a lot of nuances related to international font handling.

To use your own font you have to register it. There is one major drawback: you have to invent a font family name that’s all lowercase and without any spaces nor other special characters. So instead of font-family: 'DejaVu Sans' you have to enter font-family: dejavusans.

You can register as many font directories as you need. Moreover, you’ll need a temporary directory to store font cache. By default it’s vendor/mpdf/mpdf/tmp/mpdf/ttfontdata (assuming you’ve installed mPDF with Composer) and your script must have write permissions for that. Fortunately you can set another cache path:

use Mpdf\Config\ConfigVariables;
use Mpdf\Config\FontVariables;
use Mpdf\Mpdf;

$fontDirectory = '/home/someuser/fonts';

$defaultConfig = (new ConfigVariables())->getDefaults();
$fontDirs = $defaultConfig['fontDir'];

$defaultFontConfig = (new FontVariables())->getDefaults();
$fontData = $defaultFontConfig['fontdata'];

$mpdf = new Mpdf([
    'fontDir' => \array_merge($fontDirs, [
        $fontDirectory,
    ]),
    'fontdata' => $fontData + [
        'caslon' => [
            'I' => 'CaslonItalic.ttf',
        ],
    ],
    'tempDir' => $fontDirectory . '/tmp',
]);
$mpdf->WriteHTML($html);
$mpdf->Output('output.pdf', 'F');

When registering font files, you have to declare their style with R, B, I and BI identifiers, corresponding to “regular”, “bold”, “italic” and “bold italic” styles, respectively.

Custom fonts in TCPDF

TCPDF follows a similar font registration pattern to the previous two libraries. You can do it in two ways - either in the command line, or directly in PHP code.

Thanks to the command line you can embed the conversion commands in some Continuous Delivery pipeline that builds your application. Instead of committing the temporary font files, you can rebuild them every time with a simple command like this (assuming you’re using Composer):

php ./vendor/tecnickcom/tcpdf/tools/tcpdf_addfont.php -b -f 32 -o /home/someuser/fonts/tmp/ -i CaslonItalic.ttf

If you don’t use the command line, you can still do the same conversion thing in PHP using the TCPDF_FONTS class:

$fontDirectory = '/home/someuser/fonts/';

// The trailing slash is mandatory here
$tempDirectory = $fontDirectory . 'tmp/';

$fontname = TCPDF_FONTS::addTTFfont(
    $fontDirectory . 'CaslonItalic.ttf', 'TrueTypeUnicode', '', 32, $tempDirectory
);

$pdf = new TCPDF('P', 'mm', 'LETTER');
$pdf->AddPage();
$pdf->AddFont($fontname, 'I', $tempDirectory . $fontname . '.php');
$pdf->writeHTML($html);
file_put_contents('output.pdf', $pdf->Output('', 'S'));

The addTTFfont() method parses the original font file and creates three temporary files in the directory of your choice. Obviously, the script must have write access to that path. The return value holds a font file name which is usually a lowercase string. With AddFont() method you register the PHP font definition file created earlier.

Now you can use the font inside the document like this (remember about the lowercase font family name):

body {
  font-family: 'caslon';
  font-size: 72pt;
  font-style: italic;
}

Instead of using CSS, you can also set the current font with PHP:

$pdf->SetFont($fontname, 'I', 72);

The mysterious number 32 which appears both in the command line call and the addTTFfont() method is the font descriptor flag from the PDF specification. Fixed and italic fonts are usually autodetected, but for other types you have to specify an exact flag value:

Font descriptor flag Meaning
1 fixed font
4 symbol font
8 script (handwriting)
32 non-symbol (standard) font
64 italic font
65,536 all caps (no lowercase letters)
131,072 small caps

TCPDF does not support OpenType nor WOFF2 fonts.

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