StartDeck has a dedicated project folder for addenda.
My Google Drive > StartDeck > Projects > My Project > Addenda
PDF items uploaded to the project addenda folder are automatically appended to the project document when the document is published.
Note: PDF addenda is copied to the project folder and added to the document in the order it is uploaded to StartDeck.
Report writing tip: Use a bullet List merge field to itemize typical addenda in the report.