Generating PDFs in Drupal 7 with a custom theme. (WkHtmlToPdf only extended to make getData() public.) ALL CAPS (like MY_MODULE, NODE_TYPE_A ...) are meant as placeholders.

MODULE.php

<?php

/**
 *  Implements hook_menu().
 */
function MY_MODULE_menu() {
  $items = array();
  $items['MY_MODULE/%node'] = array(
    'access callback'  => 'MY_MODULE_access',
    'access arguments' => array(1),
    'page callback'    => 'MY_MODULE_view',
    'page arguments'   => array(1),
    'type'             => MENU_CALLBACK,
    'theme callback'   => 'MY_MODULE_theme_callback'
  );
  return $items;
}


/**
 * Access callback.
 */
function MY_MODULE_access($node) {
  $valid_types = array('NODE_TYPE_A', 'NODE_TYPE_B');

  return isset($node->type) && in_array($node->type, $valid_types) && node_access('view', $node);
}

/**
 * Menu theme callback.
 */
function MY_MODULE_theme_callback() {
  return 'MY_FRONTEND_THEME';
}

/**
 *  Implements hook_theme().
 */
function MY_MODULE_theme($existing, $type, $theme, $path) {
  $hooks = array();
  $hooks['MY_MODULE_NODE_TYPE_A'] = array(
    'variables' => array(
      'node'          => null,
      'page_title'    => '',
      'footer_text'   => '',

      'VAR_A'   => '',
      'VAR_B'    => '',
    ),
    'template' => 'templates/MY-MODULE-NODE-TYPE-A'
  );
  $hooks['MY_MODULE_NODE_TYPE_B'] = array(
    'variables' => array(
      'node'               => null,
      'page_title'         => '',
      'footer_text'        => '',

      'VAR_C'   => '',
      'VAR_D'    => '',
    ),
    'template' => 'templates/MY-MODULE-NODE-TYPE-B'

  );
  return $hooks;
}

function template_preprocess_MY_MODULE_NODE_TYPE_A(&$vars) {
  $vars = array(
    'page_title'  => 'MY TITLE',
    'VAR_A' => 'foo',
    'VAR_B' => 'bar',
  ) + $vars;
}



function template_preprocess_MY_MODULE_NODE_TYPE_B(&$vars) {

  $vars = array(
      'page_title'         => 'MY TITLE',
      'footer_text'        => 'MY FOOTER',

      'page_title'  => 'MY TITLE',
      'VAR_C' => 'foo',
      'VAR_D' => 'bar',
    ) + $vars;
}


function MY_MODULE_view($node) {

  $direct_output = variable_get('MY_MODULE:direct_output', false);
  $disable_cache = variable_get('MY_MODULE:disable_cache', false);

  $cid = "MY_MODULE:$node->type:$node->nid";
  if(!$disable_cache && ($cache = cache_get($cid))) {
    $output = $cache->data;
  }
  else {
    $theme  = 'MY_MODULE_' . $node->type;
    $html   = theme($theme, array('node' => $node));
    $output = $direct_output ? $html : MY_MODULE_generate($html);
    if(!$disable_cache) {
      $ttl = ($output === false)
        ? variable_get('MY_MODULE:cache_error_ttl', 60 * 15)
        : variable_get('MY_MODULE:cache_ttl', 60 * 60 * 6);
      cache_set($cid, $output, 'cache', time() + $ttl);
    }
  }

  if(!$direct_output) {
    header('Pragma: public');
    header('Expires: 0');
    header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
    header('Content-Type: application/pdf');
    header('Content-Transfer-Encoding: binary');
    // @todo See http://php.net/manual/de/function.strlen.php#54906 for possible problems
    // due to function overload.
    header('Content-Length: ' . strlen($output));
  }

  echo $output;
  drupal_exit();
}


function MY_MODULE_generate($html) {

  $stylesheet = DRUPAL_ROOT . '/' . drupal_get_path('theme', 'MY_FRONTEND_THEME') . '/css/pdf.css';

  $options = array(
    'no-outline', // Make Chrome not complain
    'margin-top'    => 0,
    'margin-right'  => 0,
    'margin-bottom' => 0,
    'margin-left'   => 0,
    'user-style-sheet' => $stylesheet
  );

  $options['binary'] = variable_get('MY_MODULE:binary', 'wkhtmltopdf');
  $options['tmpDir'] = file_directory_temp();

  $pdf = new \Drupal\MY_MODULE\WkHtmlToPdfPublic($options);
  $pdf->addPage($html);
  $output = $pdf->getData();
  return $output;
}