The two most used ways to attach the
documents are either by through
custom work (coding method) or by
buying plug-in.
There are lot of Extensions available inmarket but FME’s Magento Filedownload Extension is the best one toattach documents on product and CMSpages. Because This Magento moduleallows you to add files like PDF, DOCs,Excel, etc. after creating categories.
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http://www.fmeextensions.com/product-attachments.htmlOR
http://www.magentocommerce.com/magento-connect/product-attachments-file-download.html