Is it possible to make one whole file (indd) of indesign book, composed of 5 parts in the specific case?
You can use an InDesign Book file (.indb, File > New > Book...) to combine individual .indd documents.
Whether it will become a single indesign document from all the parts in the book?
I have an indesign book composed of 5 parts and I would like to merge everything into a single file
Тhis file should be indd only, not indesign book.
I'm curious WHY you need to make this into 1 file. There really is no advantage in most cases to doing that if you've been working as a Book.
Thanks for reaching out. Are you looking to merge multiple files into one? If yes, please check this similar discussion https://community.adobe.com/t5/indesign-discussions/how-to-merge-the-multiple-indesign-files-as-one/...
If that's not what you're looking for, please share a few more details about the workflow, and we'll try our best to assist you with this.