For future reference here's a complete setup guide for v1.3.x...
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1: Upload zip file to zencart/download/ (Zip files work best, use other formats at your own peril)
2: admin > catalog > option name manager
insert:
option name: Download
option type: radio/dropdown (download Option Names should be Radiobuttons or Dropdown)
3: admin > catalog > option value manager
insert:
option name: Download
option value: File
4: admin > catalog > attributes controller
select product, hit display.
Select option name (download) and option value.
Add Attributes and file name, etc...
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The next step for me is to protect my file from unpaid downloads?
AFAICT there is no code in place to do it. I am willing to write it if this is the case and will submit it as a patch.
To achieve this I would create a unique Id everytime the file was downloaded and copy it to a temp folder using the unique id as the name of the folder. Then I would delete the temp folder after the download expired. Using a cron job or checking whenever the site was accessed...
Has this or another method has already been implemented?