This app is a free tool to attach any files to an existing PDF.
You can attach any type of files to a PDF in a document/page level. If you move this PDF to a new location, the attachments move with it.
You can also add multiple file attachments, and attach a file in a specified page.

Supports remove all attachments from a PDF file, and List all attachments in a PDF file.
You can select files to attach from your local computer and from Google Drive directly.