Hybrid PDFs are a peculiar feature of LibreOffice, and are extremely handy for interoperability. They are standard PDF files, which embed a standard ODF document.
Because of this characteristic, although they have a PDF extension they can be opened by LibreOffice as fully editable documents (please note that they cannot be opened with a double click on the icon, as any regular ODF document, but they must be opened from within LibreOffice by using the menu File > Open).
The process to create a Hybrid PDF is extremely simple. In fact, Hybrid PDFs are one of the options of the menu File > Export as PDF…, which is used to create any kind of PDF file – PDF, PDF/A, signed PDF, Hybrid PDF – with LibreOffice.
Once the dialog window is open, the Hybrid PDF option is the first one on the right hand column, and can be combined with every other PDF option (which will be recognized by any PDF reader, independently from the fact that the file embeds the ODF document).