Yes, we do offer PDF sample files for most of the formats we support. The samples are very useful to understand how the PDF that you submit should look like - in particular, the dimensions including bleed.
In order to download a template:
Go to the Gelato Dashboard > Product Catalog
Find the product and the format you are interested in
Click on 3 dots next to the "Start designing" button and select"Download template"
We also offer a design editor that you can use to upload your design and create products directly from our portal.