Export a searchable PDF.

The page image plus a PDF text layer

The page image is SnapDOM's capture. The plugin places a second, invisible text layer over it using positions derived from SnapDOM's final serialized clone. No headless browser or separate layout engine rebuilds the page.

Fidelity

The visible result preserves SnapDOM's rendering of gradients, shadows, filters, web fonts and the rest of the captured element. The text layer adds document behaviour without replacing that image.

Multilingual text

CJK, Cyrillic, Greek, Arabic, Hebrew and emoji carry a /ToUnicode CMap, so selection, search and copy work for every script, whether or not a glyph travels with the file.

Pagination

Ten page sizes from A6 to tabloid, a custom [width, height] in points, or one page the size of the element. Breaks are pulled up off table rows, list items and figures, and break-before: page is honoured. Headers, footers and page numbers take their room out of the page rather than covering it. Text-form headers/footers and page numbers are real PDF text; Element-form bands are captured images.

What reaches the layer

Text nodes, input/textarea/select values, open shadow roots, and CSS transforms: rotation and skew go into the text matrix. Passwords are bulleted, never written.

What does not

Layout-hidden and transparent content is removed. Ambiguous clip, mask and filter geometry is omitted fail-safe. Arbitrary overlap is different: a rectangle or blur can cover pixels without removing the underlying semantic text, so it is not a redaction mechanism.

Embedded fonts

The faces the page painted with travel inside the file, subset to the glyphs the document actually drew. A ~320 kB face reaches a Latin page as a few kB. Turn on vectorText and eligible runs are painted as real vector glyphs instead of sitting invisible over the raster: crisp at any zoom, and an image-free export of the same page drops from ~420 kB to ~22 kB.

Fillable forms

A captured form is still a form. Inputs, textareas, checkboxes, radio groups and selects become real AcroForm fields (fillable, tabbable, extractable) carrying their name, value, options, checked state, required and read-only flags, and the accessible label as the tooltip a screen reader speaks. No JavaScript actions, no submit URLs, and a password field is written empty.

Encrypted downloads

A file that leaves the browser can be AES-256 encrypted on the way out, so the download itself is protected once it is attached and forwarded. Standard security handler revision 6, from the browser's own crypto.subtle, so no cipher code ships in the plugin and RC4 is not offered at any setting. A user password is required: the flavour of "encryption" that opens without asking is refused rather than produced.

Identity and determinism

Title, author, subject and keywords reach /Info and a mirrored XMP packet; a title also makes viewers show the document's name instead of its filename. Dates are never invented and the trailer /ID is a content hash, so the same unencrypted input produces the same bytes.

Progress, cancellation, diagnostics

Long exports report progress and take an AbortSignal. Every fidelity trade-off is also a structured diagnostic with a stable code, so a build can gate on "no annotations lost" without parsing console prose.

Transparency

A capture with alpha carries a Flate /SMask. Flatten it onto a colour to remove the mask. For every image, codec: auto compares JPEG with lossless Flate and keeps the smaller result. The lossless candidate is written in the narrowest colour space that reproduces the pixels exactly, which is one byte per pixel instead of three on the grey or few-coloured regions most page artwork turns out to be.

Document features

Headings become bookmarks and named destinations. Optional generated contents, repeated table headers, cover/back pages and watermarks make this a document exporter rather than a canvas wrapper.

Accessibility structure

Tagged output covers headings, prose, lists, tables, sections and figures. The PDF/UA-1 claim is earned, never configured: it is written only when every text operation rode an embedded face, the export is tagged, has a language and displays a title, and no painted image lacks alternative text. When a blocker remains the claim is withheld and the blocker is named.

Ships as

A minified ES module to ship, an unminified one to read, TypeScript declarations, versioned reference and MIT license. Browser use without a bundler requires an import map for the external SnapDOM peer.

Verified by

The full Chromium suite parses PDFs back with pdf.js, checks raw bytes (xref offsets, stream lengths, the lot), and one fixture compares the text layer against pixels. A separate gate imports and executes both plugin builds in Chromium, Firefox and WebKit. That is a three-engine API/artifact smoke, not three full layout suites.

Add PDF export to SnapDOM

Register the plugin once and every capture gains toPdf() alongside toPng() and toCanvas(). It reuses the existing capture rather than running a second capture engine.

import { snapdom } from '@zumer/snapdom'
import pdf from '@zumer/snapdom-plugins/pdf'

snapdom.plugins(pdf())

const shot = await snapdom(document.querySelector('#report'), {
  scale: 2, dpr: 1
})

const blob = await shot.toPdf({
  page: 'a4',                              // 'fit' | 'a4' | 'a5' | 'letter' | …
  margin: 36,                              // points
  header: { left: 'ACME', right: 'Q3 ledger' },   // real text, or pass an element
  pageNumbers: true,                        // or { format, align, size, color }
  codec: 'auto',                            // smaller JPEG or lossless Flate
  tagged: true,                            // structure, not a PDF/UA badge
  download: 'report.pdf'                   // also downloads it
})

On first PDF export, the plugin reads SnapDOM's final serialized clone, not the original live DOM, so real node removal/replacement stays aligned. Page regions are rasterized lazily and cached for later exports. Geometry-preserving final-artifact replacements stay aligned; aspect-preserving width/height scaling is allowed, while incompatible viewBox, root paint/layout or intrinsic-aspect changes fail instead of guessing coordinates. For secrets, remove or replace the node/text; never treat an overlay or blur as redaction. Capture-model options (formValues, shadow, breakAvoid, outline) belong in pdf({ ... }).

page

'fit' · one page the size of the element, or a3 / a4 / a5 / a6 / b4 / b5 / letter / legal / tabloid / executive, or [width, height] in points.

orientation

'portrait' or 'landscape'.

margin

Points. 24.

codec

auto keeps the smaller JPEG or lossless Flate image.

quality

Quality of the JPEG candidate. 0.92. It changes nothing while the lossless candidate wins, which on page artwork is until roughly 0.5.

deflate

Deflate the content streams. true.

text

Emit the selectable layer. true. Turn it off and you get an image-only PDF.

links

Emit same-document destinations and safe http:, https:, mailto: and tel: annotations. true.

image

Draw the page image. true. Set false for an image-free PDF that keeps the enabled text, links and structure. Element headers, footers and watermarks are then omitted; cover/back pages keep semantics without their raster.

formValues

Put input / textarea / select values in the layer. true.

shadow

Walk open shadow roots. true.

breakAvoid

Keep page breaks off rows, list items and figures. true.

outline

Bookmarks from headings; capture-time. true.

forms

Measure form controls so the export can write fillable fields; capture-time. true.

tagged / lang

Structure the document and set its spoken language.

embedFonts

Embed the capture's @font-face binaries, subset to the glyphs the document drew. true. 'full' embeds unsubsetted; false embeds nothing.

vectorText

Paint eligible runs as real vector glyphs instead of leaving them invisible over the raster. false. RTL and complex scripts stay on the raster.

fields

Write measured controls as real AcroForm fields. true. false keeps their values in the invisible layer instead.

repeatHeaders

Repeat a continuing table's thead pixels and text.

header

A running head across the top of every page. Give it a string or three independent segments, { left, center, right }, each of which can be a function of the page number. Either way it is drawn as real text: selectable, searchable, crisp at any zoom. Pass an element instead and it is captured, for when you need a logo. Either way it takes its height out of the printable area rather than sitting over it.

footer

The same, along the bottom.

pageNumbers

true, or { format, align, size, color, font }. Drawn as real PDF text rather than captured, so it stays crisp at any zoom and is searchable like the rest. It sits in the bottom margin, under a footer if there is one.

debugText

Paint the invisible layer in red, so you can see where it sits. false.

cover / toc / back

Captured front/back pages and generated linked contents.

watermark

Text or an element, drawn over every page.

encrypt

{userPassword, ownerPassword, permissions}. AES-256 (R6). The password is what protects the file; the permission flags are a request a viewer may honour. Needs https or localhost.

meta

{title, author, subject, keywords, creator, created, modified} /Info and XMP. Dates are written only when you pass them.

onProgress

({phase, done, total}) per step, for exports long enough to need a bar.

signal

An AbortSignal. Aborting rejects between pages with AbortError and produces nothing.

onReport

The structured diagnostics report once the Blob is finished, with stable warning codes, counts, pages, bytes, fields and annotations.

download

A filename. Downloads the blob as well as returning it.

backgroundColor

Flatten at capture, plugin-default or export time. Resolution remains a snapdom(...) concern.

Read the complete option, warning and limits reference

Included in the SnapDOM monorepo

The PDF plugin is available as MIT-licensed source in packages/plugins/pdf. PDF and Vector are available on npm in @zumer/snapdom-plugins 4.x and require SnapDOM 3.x.

Read the reference · SnapDOM on GitHub

Questions