Hi Calavaro,
You are right. That is the default fixed iframe width of popup view on PDF view, Email, Print links on the product details page of VM component which you can find in componentscom_virtuemarthelpersvmview.php file at 37th line:
if ($modal) return ‘<a class=”modal” rel=”{handler: ‘iframe’, size: {x: 700, y: 550}}” title=”‘. JText::_($altText).'” href=”‘.JRoute::_($link, FALSE).'”>’.$text.'</a>’;
That is why the popup view can’t adjust its width on different devices. Well, in this case, i suggest you to work with an experienced jQuery developer who has time and ability to customize this VM feature.
The idea is changing the fixed width x: 700 (pixels) to x: 100% so that the popup view can be responsive then. But, that parameter definition is not allowed in above line and furthermore, it will be overwritten when you update the VM component.
Note: I think you also can customize this jQuery of Email (Recommend friends) by referring the defined jQuery of Ask a question in the beginning of templatesja_hawkstorehtmlcom_virtuemartproductdetailsdefault.php file, but define with percent instead of pixel on iframe.