Question:

The Default Security of the File Name (fieldname__v) document field is configured as Editable.

When editing a document, the field does not appear on the metadata. Is there a way to update the value of this field?

Answer:

File Name (filename__v) cannot be changed. It is set by the System using the original file name if the file is uploaded by a user and the system determines the value of the document is created from a template. Hence, it is not possible to change the File Name (filename__v). 

Related Documentation:

Vault Help Documentation: Configuration Limits