Preflight Check
Preflight is the final quality-control step before a PDF goes to print. Learn what NowToPrint checks, how browser and server analysis work together, and how to fix common issues.
Preflight Check
Preflight is the final quality gate before a PDF enters production — much like the pre-flight checklist a pilot completes before takeoff. Catching errors here costs a fraction of what they cost after printing.
The 1-10-100 Rule
| Stage | Cost | Action |
|---|---|---|
| Catch error at design stage | $1 | Fix on screen |
| Catch error during preflight | $10 | Return file for correction |
| Catch error after printing | $100 | Waste paper, ink, machine time, and margin |
How Analysis Runs in NowToPrint
NowToPrint uses a browser-first analysis path so preview and fast checks can begin immediately. In supported workspace flows, if the browser runtime is incompatible or a client-side analysis crashes, the same file can be rerouted to server-side analysis instead of forcing you to start from zero.
Rust crate-owned checks
PDF domain logic now lives in NowToPrint-owned Rust crates. ntp-pdf-preflight owns preflight
findings, policy, and the public orchestration contract. ntp-pdf-core owns structural PDF truth,
and the WASM engine keeps browser, desktop, and sidecar APIs compatible. The unified
run_preflight entrypoint now delegates into the crate-owned orchestration boundary; only legacy
JSON DTO field population remains bridge debt and is not a place for new domain checks.
Result Provenance
Depending on the workflow, reports can be produced from browser-side analysis or from a server-verified analysis pass. When available, the report UI shows which path produced the final result. Server-verified workspace reports also show a capability truth map with measured, estimated, heuristic, or unsupported signals, plus safe/guided/external-only fix counts.
Provider identity
The authority fields are part of the evidence, not decoration. sourceOfTruth, providerId,
providerKind, fallbackApplied, fallbackReason, and evidenceStrength explain whether the
result came from Rust-native ntp-pdf-preflight, internal server-ts-v1/internal-analysis,
browser local-first analysis, or an external-authoritative provider. Do not read an internal
fallback as Rust-native production proof.
Preflight Passport
Server-verified Studio preflight responses include a small Preflight Passport: requestId,
pdfSha256, engineId, and lateBindingPolicy. The policy keeps originalPreserved: true and
destructiveFixupsApplied: false, so the report can prove the uploaded PDF was checked without
silently changing colour, transparency, trapping, or fonts.
Readiness is evidence-bound
A green-looking preview is not a production-ready promise. PDF Tools remains internal alpha until final gates and live smoke pass. Guarded public beta decisions require passing behavior gates, matching corpus expectations, and no unsupported capability being marketed as measured evidence.
Operator-friendly status
Studio keeps customer-facing status text in production language. Technical integration labels stay in diagnostics and audit evidence, while the workspace explains what is ready, what needs review, and whether the original PDF was preserved.
What Gets Checked
1. Image Resolution (DPI)
- Web standard: 72 DPI — too low for print, will appear blurry
- Print standard: 300 DPI minimum
- Files below 200 DPI trigger a Low Resolution error
Pixelation Risk
Images below 200 DPI produce visible pixelation in print. The system flags these as a blocking error.
2. Bleed and Safe Zone
- Bleed: Background must extend 3 mm beyond the trim line so there are no white edges after cutting
- Safe zone: Keep all important text and logos at least 5 mm from the trim line
3. Font Embedding
All fonts must be embedded in the PDF. If a font is not embedded the print shop's system may substitute a different typeface.
4. Colour Mode
- RGB — for screens (Red, Green, Blue light)
- CMYK — for print (Cyan, Magenta, Yellow, Black ink)
RGB files can be valid in modern PDF/X-4 and PDF/X-6 workflows when output intent and downstream RIP/DFE capabilities are clear. NowToPrint flags RGB or mixed colour spaces as production signals; it does not automatically force them into CMYK because early conversion can lose gamut, change transparency blending, and alter the designer's intent.
Even when a customer or operator approves a job, NowToPrint does not support RGB/spot to CMYK conversion, destructive colour conversion, transparency flattening, trapping generation, or font replacement/outlining inside the platform. These risks are reported; if that production change is truly required, upload a new PDF prepared in a specialist prepress workflow.
Interactive form fields, annotation flattening, layer merging, hairline widening, overprint edits, spot-colour remapping, and incremental-save flattening follow the same preserve-first rule: NowToPrint may report the risk, but native automatic fixes stay disabled unless a future flow has explicit approval, measured proof, and post-fix preflight evidence.
5. Document Size
Does the file size match the product ordered? An A4 PDF submitted for an A5 order is a blocking error.
6. Page Count
Booklets and books must have a page count divisible by 4 (required for folding and binding).
7. Additional Production Checks
Depending on the file and workflow, NowToPrint can also evaluate:
- trim box and media box consistency
- colour-space mix and spot-colour signals
- packaging/label technical separations such as cut, crease, white ink, varnish, foil, emboss, and braille
- packaging/label barcode quiet-zone and trim-safety signals when measured data is available
- packaging/label contour bleed, irregular shape, and open-path signals when measured data is available
- packaging/label separation proof sheet requirements for spot and finishing plates
- supplier finishing capability match for cut, white ink, varnish, foil, emboss, and braille work
- transparency and overprint risk
- page-level ink coverage and TAC alerts
- print IQ, trust, and confidence signals for review routing
Traffic Light System
NowToPrint checks files against print-production policies and returns one of three review results:
| Result | Colour | Meaning | Action |
|---|---|---|---|
| Pass | Green | Available checks passed | Continue only with required proof or handoff evidence |
| Warning | Yellow | Minor or reviewable risk | Print only with review or approval |
| Error | Red | Critical issue detected | Fix before printing |
PDF/X Standards
NowToPrint validates files against the appropriate PDF/X target and routes them to the right production decision:
- PDF/X-1a: Conservative, broad compatibility target for legacy workflows. If flattening or forced CMYK is truly required, that decision should happen in the source file or a specialist external tool, then the corrected file should be uploaded again.
- PDF/X-4: Better for modern RIPs. Preserves transparency and richer colour behaviour.
- PDF/X-6: Used in newer PDF 2.0 workflows when the downstream stack supports it.
Preserve-first policy
NowToPrint does not run RGB/spot to CMYK conversion, transparency flattening, trapping, or font conversion as automatic fixes. It also does not flatten annotations or forms, merge layers, rewrite overprint, widen hairlines, remap spot colours, or flatten incremental-save history as a native one-click fix. These operations can damage modern PDF printability. We detect them, explain the risk, and route the job to proof, review, reupload, or an external specialist tool when a legacy production constraint makes that unavoidable.
Evidence level
Not every preflight signal has the same weight. NowToPrint separates measured evidence from estimated or heuristic signals; when the server-verified path receives Rust native measurements, that provenance is preserved in the capability truth map.
Studio status dictionary
preview_ready means the file can be viewed. geometry_verified means Rust geometry matched the
loaded document. preflight_ready and preflight_blocked describe the analysis result.
Imposition states are separate: imposition_plan_ready, adjusted_plan_pending_acceptance,
accepted_plan, output_unavailable, output_ready, output_receipt_ready, proof_pending,
and production_proof_ready must not be collapsed into one “ready” label.
Studio overlays
Studio overlay targets come from canonical page geometry and finding bbox evidence. If a bbox is missing or the report/geometry hash does not match the current document, the issue stays in the panel instead of drawing a false target.
Render proof
Measured render proof only appears when a real PDFium/native renderer produces page pixels, hashed artifacts, renderer identity, PDFium revision, render profile, and sidecar runtime attestation. If that renderer is unavailable, the report says unavailable instead of treating a preview or stub renderer as proof. Studio diagnostics expose artifact type and SHA-256 summaries, but not private filesystem, bucket, or signed URL references.
Packaging and labels
For packaging and label jobs, NowToPrint classifies technical spot/separation names into Processing Steps intent signals. Missing ISO Processing Steps metadata, duplicate cut contours, or white/varnish/foil dependencies route the job to proof or specialist review instead of guessing finishing intent. Barcode quiet-zone or trim-safety risks are handled the same way: the platform asks for proof or artwork revision instead of silently moving or redrawing the barcode. Contour bleed, irregular shape, or open-path risks are routed to specialist review instead of silently changing die-line geometry. Spot and finishing separations can also require a separation proof sheet; those proof artifacts show intent without merging, flattening, or rewriting separations. Supplier finishing capability mismatches are routed before production instead of hiding the mismatch by changing the PDF.
Production intelligence
Trust Passport can carry deterministic production intelligence such as rework probability, reject
probability, supplier-fit score, press-fit score, and dispute evidence codes. These are policy
estimates, not black-box ML predictions, and they are meant to support routing, proof, and dispute
decisions before pricing automation. API polling responses can include a public trustPassport
package for completed jobs; it keeps preserve-first policy visible and does not claim render
verification unless measured PDFium render evidence is actually attached.
Benchmark claims
Benchmark and case-study artifacts separate synthetic, real-world-inspired, internal real-world, and public real-world evidence. Raw or pseudonymized customer PDFs are not eligible for public benchmark claims; public claims must come from derived fixtures, signal manifests, or licensed public files.
Outcome dashboard
Internal benchmark dashboards compare preflight risk decisions with labelled production outcomes: false positives, false negatives, reupload reduction, dispute usefulness, and calibration buckets. These are operating metrics, not public parity claims unless the sample is audited and disclosed.
Knowledge Check
Wissenscheck
When does the Preflight check run?
Which conditions trigger a Red (Error) result? (Multiple)
What is the difference between RGB and CMYK?
Common Errors and Fixes
"Low Resolution Images Detected"
Problem: Images below 200 DPI.
Fix: Source the original high-resolution image, replace in design, or reduce the element size.
"Missing Bleed"
Problem: Background does not extend beyond the trim line.
Fix: In InDesign/Illustrator set Document Bleed to 3 mm, extend background, re-export.
"Fonts Not Embedded"
Problem: Custom fonts not embedded in PDF.
Fix: In export settings enable "Embed All Fonts". If that is not possible, route the file for manual review instead of outlining the text.
"RGB Colour Space Detected"
Problem: Images or colours in RGB mode.
Fix: If colour intent is critical, prepare the file at source for the target press condition. Otherwise keep the PDF/X-4 workflow intact, preserve output intent data, and verify the downstream RIP/DFE plan. Do not use automatic RGB to CMYK conversion as a generic fix.
"Browser-side PDF Analysis Crashed Unexpectedly"
Problem: Preview loads, but browser analysis fails before the report finishes.
Fix: Refresh and retry once. In supported workspace flows, NowToPrint can reroute the same upload to server-side analysis. If the issue repeats, use the workspace analysis flow and wait for the updated result rather than re-exporting the file immediately.
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