This article applies to Classic Commerce. (Looking for Contextual Commerce documentation?)
The maximum size of a file fulfillment on a product is 5TB. The maximum file you can upload with a web browser is 5GB, but we do not recommend this method for files over 100MB. For large files, we suggest uploading via DropBox or with the Remote URL option.
In addition, you can have multiple file fulfillments on a product, and then provide multiple download links to customers in the email fulfillment.
We caution against file fulfillments that are too large as they are often difficult for many customers to download successfully, especially for customers that do not have high Internet speeds.