Can you add a Custom Field to a File/Folder in NetSuite?

@D. Orozco, you can't, but you can create a custom record to encapsulate files and folders that has a custom field. That's about as close as you can get.

I was trying to do this to assign and develop retention policies to automate file archiving. I ended up creating a custom record that had a "Document" field type for retention data related to a file, and for folders, I'm just using the folder internal ID. There's no way to "see" the details on the file or folder itself

Thanks @Michael Pope and @Dave Riccardi for the responses! Custom Record appears to be the way to go