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A render is not one engine. The worker inspects the published version’s content and dispatches to one of three pipelines. They are not interchangeable: loops and dynamic images only work on some. Choose the pipeline when you author the template, because it determines what your data can actually produce.

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How the pipeline is chosen

PipelineSelected whenEngine
PDF overlaythe template’s templateType is pdf-overlaypdfme fields on an uploaded base PDF
Document modethe content is a block layout (a pages array)@react-pdf/renderer
Canvas (Handlebars)otherwise (canvas/section content)Handlebars → HTML → Puppeteer
templateType is surfaced on GET /v1/templates/:slug. The split between document mode and canvas is decided by the stored content shape, which depends on how the template was authored.

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Capability matrix

CapabilityDocument modeCanvas (Handlebars)PDF overlay
Scalar variables✅✅✅
Loops / arrays (repeating table)❌ none✅❌ fixed fields only
Dynamic images from data❌ static src only✅ data-bound✅ data-bound (image field)
Signature image❌ (signature block is text-only)✅ via an image variable✅ via an image field
Variable-length tables❌✅❌
Best fordesigned block documentsdata-heavy docs with repeating rowsfilling a fixed PDF form
Document mode has no loop primitive and no data-bound images. A loop declared in the manifest binds at the API but renders nothing in document mode, and an image variable has no data-bound block to render it. The builder’s repeatable / table toggles are authoring hints only — they do not iterate at render time.

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Choosing a pipeline

You need a repeating table (e.g. line items, inspection areas)

Author on the Canvas (Handlebars) pipeline. It is the only pipeline that iterates a loop into repeated rows. See Variables & loops.

You need a dynamic / signature image

Use Canvas (bind an image variable) or PDF overlay (an image field). See Images & signatures.

You are filling a fixed, pre-designed PDF form

Use PDF overlay — upload the base PDF and stamp typed fields (text, image, QR) onto it.

It is a designed block document, no arrays

Document mode is the simplest and the default of the modern builder.
Migrating a template from canvas content to a document-mode block layout removes loop and dynamic-image support. If a template relies on either, keep it on the canvas pipeline.