It isn't a hidden file. It’s simply a result of how the system converts binary attachments (like PDFs or images) into plain text for public record.
Ever wondered about the "6eq.7z" string in SEC filings? 6eq.7z
In these documents, it is part of a (Unix-to-Unix encoded) text block used to transmit binary data over text-based systems. It is not a functional file you can download or open. It isn't a hidden file