AFAIK you are limited to the predefined Tokens.
The only way (I know) to download the file is by going to your order history.

You can see a listing of all of the available e-mail tokens in the documentation below:

https://hotcakescommerce....Mail-Template-Tokens

In short, you can't display the download link in an e-mail easily, unless you choose to override the e-mail task in your own custom order workflow task. Documentation on custom workflows is below:

https://hotcakescommerce....r-Workflow-Solution-

Then, you'd implement something like this, but inject the download link:

https://hotcakescommerce....ers-Programmatically

In closing, I'd like to say that we'd suggest against this approach since you lose the huge opportunity of additional branding, upsell/resell, value proposition, privacy/security, and analytics that you get by simply redirecting the customer back to your website to view and click on the download link. In general, it's always a best practice to keep sending your customers and prospective customers to your website for everything that you can.