What is a PDF Portfolio or PDF Package?
A PDF Portfolio contains multiple files assembled into an integrated PDF unit. The files in a PDF Portfolio can be in a wide range of file types created in different applications. For example, a PDF Portfolio can include text documents, e-mail messages, spreadsheets, CAD drawings, and PowerPoint presentations. The original files retain their individual identities but are assembled into one PDF Portfolio file. You can open, read, edit, and format each component file independently of the other component files in the PDF Portfolio.
For best performance, keep the total number of component files at 15 or less, and the total size of all component files under 50 MB.
Reference link: Adobe Documentation
This format is a great way to share files in a single packaged content.
Should I use it?
PDF Portfolios or Packages should NOT be used for delivery or accepted as an alternative to native files or productions.
Although PDF Packages or Portfolios are an easy-to-use format, there are many flaws with this type of format for the e-discovery market.
1) The storing of metadata and notes at the top level of the Portfolio causes Accessdata software to decide to include all files within a Portfolio as a complete family. I.e. all objects in the Portfolio are considered child objects to the Portfolio.
2) The ability to edit the metadata stored in this file type is another reason why Accessdata does not recommend this file type as an alternative to native file productions.
Adobe has an example type attached here: PDF Portfolio Example