To make sure - do you want to place there list of attached file names, or you want to link the files?
In case of names you could do as Karol said - prepare buisness rule, and use it.
I'm not sure if there is a way to make link in word using designer studio though.
If you will be trying to make it work with linking - url for downloading attachments looks like this:
https://serverinstance/WEBCONBPS/api/nav/db/1/attachments/attachmentID/download - it will download latest version of the attachment.
You will need to query [BPS_Content].[dbo].[WFDataAttachmets] (list of current attachments), and maybe look at [BPS_Content].[dbo].[WFHistoryAttachments] (versioned list of attachments), and [BPS_Content_Att].[dbo].[WFAttachmentFiles] (base64 encoded attachments content) too.
Comments are stored in [BPS_Content].[dbo].[WFElements] under WFD_Description column. You will have to process it though, as they are not stored in separate rows.