Split Documents

I would like to be able to mark a document into equal parts by word count with a variable number of equal parts depending on the document. For example, a document may have 78485 words and I would like this particular document to be marked in sections of four into equal sections of about 19621 words with an easily findable mark (probably something with find function). Then I may have a document of 102363 words that I would like to mark in the same fashion but into six equal sections of 17060. The number of sections will vary depending on the document. I am using MS Word 365 on a Mac.