Hey Mark,

They're not necessarily bad for the customer as most phones can handle PDF files.

However, as a designer, developer and/or restaurant owner, you can give your customer a better experience if you've designed a responsive page for it instead. A PDF takes them away from the interface you've created on the website. It takes them away from the "make a reservation" button or the clickable telephone number to get your delivery.

Also, for restaurants with menus that change frequently, uploading new PDFs and making sure the old ones are deleted can be a bigger process than changing one or two lines in a WYSIWYG editor or a custom field.