Note attachment (e.g. pdf) is stored locally (physically) in App\Profile\Databases\Attachments location of Windows Evernote App. Annotating of the file (e.g. in Adobe reader) followed by replacing of the file in the location is present / visible in the app as it is reading directly from App\Profile\Databases. The attachment containing (new) annotation is synched without any issues. Android Evernote app seems not to have such local database directory where attachments are stored physically. If it does, replacement of the attachment would do the job I suppose.