What files does a print-on-demand service actually need?

Almost always two separate print-ready PDFs: an interior file and a cover file. The interior (sometimes called the book block) contains all your pages in order — title page, front matter, body, back matter — sized to the book’s trim. The cover is usually a single "wrap" PDF that lays out the back cover, the spine, and the front cover as one continuous piece, because the press prints it as one sheet and folds it around the block. They are prepared differently (the cover needs bleed and a spine; the interior usually does not need bleed unless it has edge-to-edge images), which is why services ask for them separately. The first thing to do before formatting anything is to find the specific platform’s file requirements and, ideally, download its template — every print-on-demand service publishes one, and building to it from the start saves a lot of rework.

How do I choose and set the trim size?

Pick a trim size from the platform’s list of supported sizes, then build both PDFs to it exactly. Trim size is the finished physical dimensions of the book, and it is the foundational decision because margins, spine width, and image requirements all depend on it. Common book trims include sizes like 5"×8", 5.5"×8.5", and 6"×9", but what matters is choosing one your print-on-demand provider actually supports, because an unsupported size is a non-starter regardless of how good your file is. Once chosen, set your interior PDF’s page size to that trim (plus bleed only if you have edge-to-edge interior images), and use it as the basis for calculating the cover’s overall dimensions. Decide the trim first; everything else is derived from it.

How is the spine width determined, and why does page count matter?

The spine width is calculated from your final page count multiplied by the thickness of the paper stock, so you cannot finalise the cover until the interior is finished. More pages on a given paper means a thicker book and a wider spine; switch paper weight and the spine changes too. This is why print-on-demand services give you a spine-width figure (or a cover-template generator) only after you tell them the page count and paper choice — and why you must lock the interior PDF before designing the cover wrap. If you change the page count later (add a chapter, adjust front matter), the spine width changes and the cover must be regenerated, or your title will be off-centre on the spine. Finalise the interior, get the exact spine width from the platform, then build the cover to match.

What are the margin and bleed rules for the interior?

Two things: a generous inside (gutter) margin that grows with page count, and bleed only where content runs to the edge. The gutter is the inner margin near the binding; because a thicker book does not open as flat, more pages need a larger inside margin so text does not disappear into the spine — print-on-demand services specify a minimum gutter that increases with page count, and you should follow their table. Outer, top, and bottom margins keep text a safe distance from the trimmed edge so nothing is cut off. Bleed (extending content past the trim) is only needed in the interior if you have images or color that go edge-to-edge; a normal text interior with white margins does not need interior bleed. Follow the platform’s exact margin and bleed minimums — they are the most common cause of a rejected interior.

What makes a print-on-demand PDF get rejected?

The recurring culprits are missing fonts, low-resolution images, wrong size or missing bleed, and insufficient gutter margins. Fonts not embedded mean the press cannot reproduce your type, so embed (and subset) every font. Images below roughly 300 DPI at print size come out soft, so check resolution at the placed size. A PDF whose page size does not match the chosen trim, or a cover without the required bleed, fails the platform’s preflight. And text too close to the spine or trimmed edge — too small a gutter or outer margin — triggers rejection or an ugly result. The way to avoid all of these is to build to the platform’s template, run its preflight/previewer before submitting, and order a physical proof: print-on-demand services let you review a proof copy, and seeing the real book catches problems no on-screen check will.

Is it safe to prepare my manuscript with an online tool?

Use a tool that runs on your own device for an unpublished manuscript. Your book interior is unreleased work you presumably do not want sitting on a third-party server, yet many online prep tools upload your file. Client-side (in-browser) tools handle print prep — embedding fonts, setting page size, adding bleed, checking resolution — locally so the manuscript never leaves your computer, and ScoutMyTool’s print-on-demand prep works this way. Confirm a tool is client-side before uploading, or use offline software. And whatever you use, the final safeguard is the platform’s own proof: review the on-screen preflight and order a printed proof before you publish, because that is the only way to be certain the book is right.

8 min read

How to use a PDF as a print-on-demand product (Lulu, Amazon KDP)

By ScoutMyTool Editorial Team · Last updated: 2026-05-21

The first book I tried to self-publish bounced off the platform’s preflight four times — wrong trim, no bleed on the cover, a spine that did not match my page count, fonts not embedded. Each rejection taught me the same lesson: print-on-demand is not "upload your PDF and go," it is preparing two specific, print-ready PDFs to a platform’s exact specification. Get an interior file and a cover wrap built to the right trim, bleed, margins, spine width, and font settings, and services like Amazon KDP or Lulu turn your manuscript into a real book on demand. This guide is the prep checklist I wish I had started with — what files you need, how the pieces are derived from your trim and page count, and the catches that cause rejections.

Interior vs. cover — what each PDF needs

Item	Interior (book block)	Cover (wrap)
What it is	The book block (all your pages)	A single wrap: back + spine + front
Trim size	Matches the chosen book size	Full wrap width = back + spine + front + bleed
Bleed	Only if interior images go to the edge	Almost always — art runs to the edge
Margins	Inside/gutter margin grows with page count	Keep text clear of the spine and trim
Spine	n/a	Width computed from page count × paper thickness
Fonts / resolution	Embedded fonts; ~300 DPI images	Embedded fonts; ~300 DPI; CMYK if required

Exact numbers (margins, bleed, spine) vary by platform and paper — always use the specific service’s published template and spec.

Step by step — prepare a POD-ready PDF

Get the platform’s spec and template first. Download the service’s template for your chosen trim and read its file requirements before formatting anything.
Choose a supported trim size. Pick from the platform’s list; build the interior to that exact size (plus bleed only for edge-to-edge interior images).
Set margins, with a gutter for the page count. Follow the platform’s minimum inside/gutter margin (it grows with pages) and outer margins so nothing is cut or lost in the spine.
Finalise the interior, then get the spine width. Lock the page count, then use the platform’s figure or cover generator to size the spine and build the cover wrap with bleed.
Embed fonts and check image resolution. Embed (subset) all fonts and confirm images are ~300 DPI at print size; export to the platform’s required format (often PDF/X).
Run preflight and order a proof. Pass the platform’s online previewer/preflight, then order a printed proof and check the real book before publishing.

The principle: build to the spec, prove on paper

Print-on-demand rewards two disciplines. The first is building to the platform’s specification rather than to a generic idea of "print-ready" — every service publishes exact trim sizes, margin and bleed minimums, a spine formula, and file-format requirements, and a file that ignores them gets rejected at preflight no matter how good it looks. Download the template and build to it from the start. The second is proving on paper: the on-screen previewer catches structural problems, but only a physical proof copy reveals how the book actually reads, how the cover wraps, whether the spine text is centred, and how the images really print. Almost every avoidable self-publishing disappointment comes from skipping one of these — guessing at the spec, or publishing without a proof. Build to the spec, finalise the interior before the cover, and order the proof, and your PDF becomes a book you are proud to sell.

FAQ

What files does a print-on-demand service actually need?: Almost always two separate print-ready PDFs: an interior file and a cover file. The interior (sometimes called the book block) contains all your pages in order — title page, front matter, body, back matter — sized to the book’s trim. The cover is usually a single "wrap" PDF that lays out the back cover, the spine, and the front cover as one continuous piece, because the press prints it as one sheet and folds it around the block. They are prepared differently (the cover needs bleed and a spine; the interior usually does not need bleed unless it has edge-to-edge images), which is why services ask for them separately. The first thing to do before formatting anything is to find the specific platform’s file requirements and, ideally, download its template — every print-on-demand service publishes one, and building to it from the start saves a lot of rework.
How do I choose and set the trim size?: Pick a trim size from the platform’s list of supported sizes, then build both PDFs to it exactly. Trim size is the finished physical dimensions of the book, and it is the foundational decision because margins, spine width, and image requirements all depend on it. Common book trims include sizes like 5"×8", 5.5"×8.5", and 6"×9", but what matters is choosing one your print-on-demand provider actually supports, because an unsupported size is a non-starter regardless of how good your file is. Once chosen, set your interior PDF’s page size to that trim (plus bleed only if you have edge-to-edge interior images), and use it as the basis for calculating the cover’s overall dimensions. Decide the trim first; everything else is derived from it.
How is the spine width determined, and why does page count matter?: The spine width is calculated from your final page count multiplied by the thickness of the paper stock, so you cannot finalise the cover until the interior is finished. More pages on a given paper means a thicker book and a wider spine; switch paper weight and the spine changes too. This is why print-on-demand services give you a spine-width figure (or a cover-template generator) only after you tell them the page count and paper choice — and why you must lock the interior PDF before designing the cover wrap. If you change the page count later (add a chapter, adjust front matter), the spine width changes and the cover must be regenerated, or your title will be off-centre on the spine. Finalise the interior, get the exact spine width from the platform, then build the cover to match.
What are the margin and bleed rules for the interior?: Two things: a generous inside (gutter) margin that grows with page count, and bleed only where content runs to the edge. The gutter is the inner margin near the binding; because a thicker book does not open as flat, more pages need a larger inside margin so text does not disappear into the spine — print-on-demand services specify a minimum gutter that increases with page count, and you should follow their table. Outer, top, and bottom margins keep text a safe distance from the trimmed edge so nothing is cut off. Bleed (extending content past the trim) is only needed in the interior if you have images or color that go edge-to-edge; a normal text interior with white margins does not need interior bleed. Follow the platform’s exact margin and bleed minimums — they are the most common cause of a rejected interior.
What makes a print-on-demand PDF get rejected?: The recurring culprits are missing fonts, low-resolution images, wrong size or missing bleed, and insufficient gutter margins. Fonts not embedded mean the press cannot reproduce your type, so embed (and subset) every font. Images below roughly 300 DPI at print size come out soft, so check resolution at the placed size. A PDF whose page size does not match the chosen trim, or a cover without the required bleed, fails the platform’s preflight. And text too close to the spine or trimmed edge — too small a gutter or outer margin — triggers rejection or an ugly result. The way to avoid all of these is to build to the platform’s template, run its preflight/previewer before submitting, and order a physical proof: print-on-demand services let you review a proof copy, and seeing the real book catches problems no on-screen check will.
Is it safe to prepare my manuscript with an online tool?: Use a tool that runs on your own device for an unpublished manuscript. Your book interior is unreleased work you presumably do not want sitting on a third-party server, yet many online prep tools upload your file. Client-side (in-browser) tools handle print prep — embedding fonts, setting page size, adding bleed, checking resolution — locally so the manuscript never leaves your computer, and ScoutMyTool’s print-on-demand prep works this way. Confirm a tool is client-side before uploading, or use offline software. And whatever you use, the final safeguard is the platform’s own proof: review the on-screen preflight and order a printed proof before you publish, because that is the only way to be certain the book is right.

Citations

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