List of steps to reproduce (step by step, including full links if applicable):
- Go to any old revision of a page
- Click "Download as PDF"
What happens?:
You are sent to Special:Book, which at least in the case of enwiki means an error message saying to download as PDF instead.
What should have happened instead?:
I don't know whether DownloadAsPdf supports old revisions—it should, but if not, that's a feature request, not a bug. But if it does, then clicking "Download as PDF" should take you to that, and if it doesn't, the option should just not be there.