In this class app/code/core/Mage/Catalog/Block/Navigation.php in this method:

/**
 * Render category to html
 *
 * @param Mage_Catalog_Model_Category $category
 * @param int Nesting level number
 * @param boolean Whether ot not this item is last, affects list item class
 * @param boolean Whether ot not this item is first, affects list item class
 * @param boolean Whether ot not this item is outermost, affects list item class
 * @param string Extra class of outermost list items
 * @param string If specified wraps children list in div with this class
 * @param boolean Whether ot not to add on* attributes to list item
 * @return string
 */
protected function _renderCategoryMenuItemHtml($category, $level = 0, $isLast = false, $isFirst = false,
    $isOutermost = false, $outermostItemClass = '', $childrenWrapClass = '', $noEventAttributes = false)
{
    if (!$category->getIsActive()) {
        return '';
    }
    //...
}

the first parameter $category has type Mage_Catalog_Model_Category. I need to get the value of the custom category attribute inside that method. But when I try to get the category attribute value like this:

$value = $category->getData('catalog_pdf');

it returns nothing. I checked the type of the parameter $category with

get_class($category); //It returnes Varien_Data_Tree_Node

and it turned out to be Varien_Data_Tree_Node (but not Mage_Catalog_Model_Category like it is declared in the comments above this method).

So my question is:

1. How I can retrieve an object of type Mage_Catalog_Model_Category so that it is possible to retrieve value of the category attribute? Is the standard category object wrapped somehow inside that object of type Varien_Data_Tree_Node?

2. And a bonus question: what is that type Varien_Data_Tree_Node used for? I tried to investigate the code but that class seems to be quite complicated. If anyone knows any good tutorials about it, I'd be very grateful.