how to create a multiple page pdf document

I want to create a multi page pdf file. How is that accomplished?

Creating a new PDF document and adding pages to an existing one are two different things. Edit your question to better describe your goal. While at it, mention your OS name and LO version.

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If you’re creating the document from scratch in Writer, simply write your text, with any special pagination, graphics, tables, etc. in the normal way. For easy re-editing, save your original document in .odt format (i.e. as an ODF Text Document). Then go to File > Export As > Export as PDF…, or alternatively File > Export As > Export Directly as PDF. The first option gives you more control of your PDF file settings.

If you are editing an existing PDF, for which no .odt or .doc original exists, then the procedure is less straightforward. Opening your PDF in LibreOffice will bring it up as a Drawing. New pages will have to be added manually, as will the layout of text boxes and graphics. It could get painful! In this case, a more specialised PDF editor program might be preferable.