Windows issue for Magento2
https://magento.stackexchange.com/questions/224912/magento-2-2-4-white-blank-page-after-setupdicompile-on-windows-10

https://inchoo.net/magento-2/magento-2-custom-widget/
https://webkul.com/blog/overriding-rewriting-classes-magento2/
https://magento.stackexchange.com/questions/85679/change-product-price-on-selection-of-custom-option-checkbox

$page->setFillColor(new \Zend_Pdf_Color_Rgb(0.93, 0.92, 0.92));
https://stackoverflow.com/questions/6096370/a-small-zend-pdf-color-rgb-problem
https://magento.stackexchange.com/questions/252875/how-to-override-vendor-magento-module-sales-model-order-pdf-items-invoice-defaul
https://magento.stackexchange.com/questions/240100/magento-2-changing-the-packing-slip-pdf-print-out-layout
https://magento.stackexchange.com/questions/212330/magento-2-change-invoice-pdf-font-and-add-logo-and-mailing-address-in-footer