Question: Our client has several specification sheets in pdf format for many of their products. What is the best or easiest way for them to add a downloadable PDF to each product page. (Some PDFs fit many products).

UPDATE: I found a very useful extension for this <http://amasty.com/product-attachments.html>

Answer: 
you can use this extension for product pdf [Pdf Extension](http://www.magentocommerce.com/magento-connect/product-attachments-extension.html)

This extension allows assigning multiple pdf file to your product, pdf can be uploaded and then assign in product is very easy
Another possibility is to use an extension which does exactly what you want to do.
There exists a free extension for this purpose:

<http://www.magentocommerce.com/magento-connect/pdf-for-every-product-8631.html>

Another one which is free for up to 1000 products is this one:

<http://www.magentocommerce.com/magento-connect/pdf-for-every-product-8631.html>