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: 
A simple way to do this, without much programming, is to take advantage of magento's product attributes. It's very simple to do the following -

1. add a product attribute called "spec\_sheets" and allow that attribute to used on the front end. Then add that attribute to the appropriate product attribute sets.
2. have your client FTP the pdf files to a directory under your magento install - say media/specs.
3. edit the product(s) where the spec sheets should be shown and enter the pdf file names.
4. Update the product view template to detect if the attribute has a value by getting it's value, $\_product->getSpecSheet(). If a file exists in media/specs directory with the same name as the attribute, display a link to the PDF on the product page.

If there are more than 1 PDF per product, then you can have the admin enter the filenames in a comma separated list and then use php to parse out the individual filenames.
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