Most of what makes a self-published paperback look self-published is not the cover. It is half a dozen interior conventions that traditionally published books follow without drawing attention to themselves, and that word processors do not do by default.
None of them are difficult. They are just invisible until you know.
Chapters open on the right
In a printed book, chapters begin on a recto — a right-hand page. Open any novel and check; it will be true for almost all of them.
This has a consequence people try to avoid and shouldn't: when a chapter ends on a right-hand page, the following left-hand page is blank. Not blank with a page number and a running head — genuinely blank.
That empty page is correct. It is not wasted space or a formatting error, and trying to eliminate it by shuffling text is how interiors end up looking strange. Roughly half your chapters will produce one.
Non-fiction is sometimes more relaxed about this, letting chapters open on whichever side falls next to save pages and therefore printing cost. Fiction almost never is.
Chapters open low on the page
A chapter's first page does not start at the top margin. The heading sits some way down — commonly a quarter to a third of the way — with the text beginning below it.
The space is called sinkage, and it is doing something: it signals a break. A reader turning to a chapter opening knows instantly what it is without reading a word, because the shape of the page is different from every other page.
A chapter heading tight against the top margin is one of the clearest tells of an unformatted interior.
The first page of a chapter has no running head
Running heads are the small lines at the top of each page carrying the author's name, the book's title, or the chapter's. They are helpful when you have flicked to the middle and want to know where you are.
They are suppressed on chapter openings, and on any full-page display element — the title page, the copyright page, a part divider. The reason is straightforward: a chapter opening announces itself. A running head on top of it is redundant, and it competes with the sinkage that is doing the announcing.
The same applies to the page number on those pages. Which brings us to the part that genuinely confuses people.
Page numbering is not one sequence
A printed book has two numbering systems.
Front matter — title page, copyright, dedication, contents, foreword — is numbered in lowercase roman numerals: i, ii, iii, iv. The pages are counted from the very first leaf, but the numbers are usually not printed on the display pages. So the first printed number a reader sees might be "vii" on a contents page.
The body restarts at arabic 1, on the first page of chapter one. Not continuing from the front matter — restarting.
This is why "the page numbers are wrong" is such a common complaint about self-published interiors. Word will happily number a document 1 to 312 straight through, which produces a book whose chapter one starts on page 9.
The mechanism in Word is a section break between the front matter and the body, with the body section set to restart numbering at 1 and to use arabic numerals. Not a page break — a section break. They look identical and only one of them works.
Where the numbers go
Bottom centre, or bottom outside corner. Both are conventional; pick one and never vary.
Bottom outside is slightly more useful for thumbing through, since the number is where your thumb already is. Bottom centre is simpler and forgiving of a misjudged margin.
Top corners work too, but they compete with running heads and are harder to get right.
None of this applies to ebooks
Every convention above is about physical pages, and a reflowable ebook does not have any. No recto and verso, so nothing opens on the right. No fixed pages, so no numbering and no running heads.
An ebook signals a chapter differently: each one is its own section in the file, which is what makes the Go To menu and the progress bar work. Carrying print furniture into an ebook — a typed contents page with page numbers, running heads — produces clutter that means nothing. See reflowable or fixed layout for why.
Doing it without doing it by hand
All of this is achievable in Word: section breaks, mirrored margins, different first-page headers, restarting numbering. It is fiddly rather than hard, and it is the kind of fiddly where one wrong setting is invisible until the proof arrives.
Our print book formatter applies these conventions by default — chapters opening recto with sinkage, running heads suppressed where they should be, front matter and body numbered separately, and the mirrored margins from book margins and gutters. Upload a .docx and read the result before deciding anything.