...not easily that is for sure, the book function was developed for merging separate multipage documents together, allowing auto numbering without the need to be manually shuffling pages from one document to another...
...manually using the pages palette is the only function I'm aware of, drag and drop the pages in sequences into one document, but caution is probably advised when using this method...
...I'd keep your documents together utilizing the book function, print the whole book to postscript and distill to pdf to have all in one completed document as an end product...
Andrew