In Projects, once a document is uploaded, how can I edit or add a new tag?

In Projects, once a document is uploaded, how can I edit or add a new tag?

I have several different types of documents in my Projects documents folder.

I have added some new tags but I don't see how to edit tags on existing documents or even edit comments. Also, if it requires using other Zoho apps, what can I do with the PDF files, which aren't editable in Viewer?

Thanks

Stan