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
[Here's MagDoc Module](http://www.magentocommerce.com/magento-connect/sp-magdoc-8372.html) which helps to manage your PDF or any other types of file on Scribd and display that document on browse by adding few codes. Hope this helps.