Document Id Unique

Hi There, I am working on creating a package with a document that has an Id assigned to it: .withDocument( newDocumentWithName( "Second Document" ) .fromFile( "src/main/Resources/document.pdf" ) .withId( documentId ) I was wondering if this Id needs to be globally unique among all packages? Or does it have to be unique only for that package? I want to use this Id to download the signed file later using the following function: byte[] pdfDocumentBytes = eslClient.downloadDocument(packageId, documentId);