You can upload a file to link to each item when the user clicks the 'View PDF' link. The whole process is quite easy and doesn't require anything more than you uploading a file.
Step 1. Create your file
Firstly you will need to create your pdf. Once you have done so you will need to name it accordingly. the naming convention is sitename_sku.pdf
If you do not know your sitename it is the name that follows http://secure.zeald.com/ on secure links. To find this out you can log into the backend of your website (www.yoursite.com/admin/login) and when you're in the backend check the url in your browser:
In this case if our item had a SKU of 00911 the filename would be: zhelp_00911.pdf
Step 2. Upload your file
The next (and final) step is to upload your PDF to the items folder. More information on uploading files can be found here
And you're done!
The file will now automatically be linked to the 'View PDF' link on the items page.
(if you can't see the 'view pdf' link on the product page, check that it's turned on under the pencil tool of either the product_view component or the product_links component, depending on if you have the upgraded layout or not).