You may have seen attempts to upload multipage documents as a series of individual files.
This can be done but the results are seldom satisfactory to you as the reader. You read a page and then you need to find a file containing the next page and then find the next page, etc. This is very awkward.
The idea is excellent, but the method is flawed, Ideally you will convert the multipage document to PDF format so that the whole book is a single file. PDF also has the advantage of being able to use a variety of different fonts and layouts including images. Images take up a lot of storage apace, but 2000 pages of text can easily fit within the 15 GB size limit allowed by FamilySearch.
If you have written a book. create a PDF copy from your word processor by using File > Save As or File > Export, or File > Print > Print to PDF. Then upload the PDF file to FamilySearch memories.
For example, see "Ancestors of Ernest (Robert) Kinney"
https://www.familysearch.org/tree/person/memories/L492-3Z6
(This is a short book, generated by genealogy software and enhanced in a word processor.)
If you want to create a PDF from a series of separate page images (eg. JPEGs), the process is more complicated, If your scanner has the option, load the pages into the document feeder and choose Scan to PDF. Then run the resulting file through Optical Character Recognition to convert the images of text to actual text, greatly reducing the file size.
Alternately, you can import the page images into the word processor and export the file as PDF, The page images take up a lot of storage apace, creating a huge file, but OCR may reduce it to a usable size.
If OCR software did not come with your scanner, there are sites online that do OCR conversions,