Workaround for Magestore Giftwrap

1. Open the following file: app/code/local/Magestore/Giftwrap/etc/config.xml 

2. Edit the file to delete the following code: 

<sales>
	<rewrite>
		<order_pdf_invoice>Magestore_Giftwrap_Model_Sales_Order_Pdf_Invoice</order_pdf_invoice>
	</rewrite>
</sales>
<sales>
	<rewrite>
		<order_pdf_shipment>Magestore_Giftwrap_Model_Sales_Order_Pdf_Shipment</order_pdf_shipment>
	</rewrite>
</sales>

3. Save the edited file 

4. Refresh your Magento cache for the changes to take effect.