How do I edit PDF metadata?
Try AutoMetadata (free for both commercial and non-commercial use)
AutoMetadataâ„¢ is a free standalone application for exploring and editing metadata, document properties and viewer preferences in multiple PDF documents.
The key feature is ability to select many PDF files and folders and quickly inspect and update information in all documents with a minimal effort.
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Not to mention that this software is free for both commercial and non-commercial use.

Editing Document Metadata
You can either edit metadata in place or perform a search and replace operation on selected fields. Use this operation to update multiple PDF documents with a common metadata change.
Source AutoMetadata
Disclaimer
I am not affiliated with AutoMetadata
in any way.