There are already services to collect geographic information from IP addresses, and if you required your subscribers to register with a zip (or postal) code, then you’d have a more reliable source of geographic information associated with each customer. Instead of building your PDF eZine once, you’d have to have the customer log-in and download it, and the Distiller Server would be scripted to customize it and swap in the relevant page of ads.

One related example, is how RPGNow.com watermarks the PDF products it sells. I don’t know what they’re using on the back end, but it is actually adding a small text line to the bottom of each page with the purchasers name and transaction ID number, before distilling the product as a PDF and serving it. This would be similar, but instead of a little watermark tag, it would be an ad swap.

When it comes to technology like this, it’s just a matter of money. Getting the service firm or professionals to put it together for you. The harder, and more interesting part, would be in building the advertisement / marketing network to gather the targeted ads and local advertisers to participate in your program.

In conclusion: totally doable with current products.