What it means
Preflight is borrowed from aviation: the checklist run before take-off. In print it is the inspection of a PDF against the printer's specification before any paper is committed. Software (Acrobat's Preflight tool, Enfocus PitStop, or the printer's own upload system) opens the file and reports every deviation: fonts not embedded, images below 300 dpi, RGB or spot colours where CMYK is expected, missing bleed, a page size that doesn't match the order, a page count that isn't even, hairlines too thin to print, ink coverage too high, transparency that will flatten badly.
A preflight report is not a judgement on the book; it is a list of things that would print wrong. Some printers normalise minor issues automatically (converting colour, adding bleed by mirroring), others reject the file and wait.
Running your own preflight before uploading, and reading the printer's report rather than clicking past it, is the difference between a proof that surprises you and one that doesn't.
In Bindery
Bindery validates its PDFs against Lulu’s own rules — trim, bleed and spine width from the real page count — before anything prints.
Make the book, not the checklist
Describe a book or upload a manuscript. Bindery writes with you, typesets in LaTeX, sizes the spine from the real page count and produces printer-validated files — the watermarked proof is always free.
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