This is an example of the showText() method for drawing text on a surface. Note that selectFontFace() will select fonts that your OS recognizes and I didn't see a way in the current API to select a font by filename.
<?php
$surface = new CairoImageSurface(CAIRO_FORMAT_ARGB32, 960, 250);
$ctx = new CairoContext($surface);
$ctx->selectFontFace('EuropaGroNr2SH-XBolCon');
$ctx->setFontSize(30);
$ctx->setAntialias(1);
$ctx->moveTo(0, 44);
$ctx->showText('Hello,');
$ctx->moveTo(30, 74);
$ctx->showText('world!');
$sName = tempnam('/tmp','hello');
$surface->writeToPng($sName);
$data = file_get_contents($sName);
unlink($sName);
header('Content-Type: image/png');
echo $data;