Well, it could be the background picture for your template, but you will need to convert it to the right file type. This is from the knowledgebase article found here (https://help.docebo.com/hc/en-us/articles/360020084280-Creating-and-Managing-Certificates)

• The background image size cannot be more than 2560x1810px and 10MB
• The supported image formats are JPG, PNG, JPEG, GIF
• Images with transparency are not recommended

Once converted you will need to use the designer to place the placeholder data for the certificate.

Good luck!

Might want to work with the team to designing it together so that majority is background image, but is easy to add a table or similar on top of it to add the content, and if so you might want them to treat it and approach it as designing an old Email, a lot of the practices and templates from those old setups help out a lot with templates here.