There is a huge difference between using standard software to design a book, and doing it in a truly professional manner. POD vendors usually have their own software which can be downloaded free of charge and then used to place text and images in one of their standard templates. The selected template determines parameters such as page layout, background colour, margin size, fonts, locations of titles, headers and footers, paragraph indentations, the positions and sizes of images etc. This approach may lead to an acceptable book design but the finished book will be recognized very quickly by an experienced eye as a product of a "standard" POD template.
There are basically two options for designing a POD book and the choice must to some extent be dependent upon the selected POD vendor. The first is to accept the vendor's standard style and presentation, which may allow a few basic parameters such as page size to be chosen but not much more. The text of the book is uploaded as a word-processor file and is converted to a PDF using one of the vendor's standard templates.This is usually the cheapest approach because preparation work is minimized.
The second approach leaves all the design and layout work in the hands of the author. The vendor typically offers a range of standard page sizes from which the author can make a selection. The available space is used as required, and the completed PDF is then uploaded to the printer who takes no responsibility for errors omissions etc.