<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <preference for="MagentoSalesModelOrderPdfItemsInvoiceDefaultInvoice" type="MycompanyTaxModelOrderPdfItemsInvoiceDefaultInvoice" />
    <preference for="MagentoSalesModelOrderPdfInvoice" type="MycompanyTaxModelOrderPdfInvoice" />

/**
     * Set font as regular
     *
     * @param  Zend_Pdf_Page $object
     * @param  int $size
     * @return Zend_Pdf_Resource_Font
     */
    protected function _setFontRegular($object, $size = 7)
    {
        $font = Zend_Pdf_Font::fontWithPath(
            $this->getFontsDir() . ('dejavu-sans/DejaVuSansCondensed.ttf')
        );
        $object->setFont($font, $size);
        return $font;
    }
    /**
     * Set font as bold
     *
     * @param  Zend_Pdf_Page $object
     * @param  int $size
     * @return Zend_Pdf_Resource_Font
     */
    protected function _setFontBold($object, $size = 6)
    {
        $font = Zend_Pdf_Font::fontWithPath(
            $this->getFontsDir() . ('dejavu-sans/DejaVuSansCondensed-Bold.ttf')
        );
        $object->setFont($font, $size);
        return $font;
    }

    /**
     * Set font as italic
     *
     * @param  Zend_Pdf_Page $object
     * @param  int $size
     * @return Zend_Pdf_Resource_Font
     */
    protected function _setFontItalic($object, $size = 7)
    {
        $font = Zend_Pdf_Font::fontWithPath(
            $this->getFontsDir() . ('dejavu-sans/DejaVuSans-Oblique.ttf')
        );
        $object->setFont($font, $size);
        return $font;
    }