klz-cables.com/scripts/inject-letterpress.ts

import { PDFDocument, PDFName, PDFString, PDFNumber, PDFDict, PDFArray } from 'pdf-lib';
import fs from 'fs';
import path from 'path';

async function run() {
  const filePaths = [
    'KLZ_Visitenkarte_Michael_Bodemer_Viaprinto_CMYK.pdf',
    'KLZ_Visitenkarte_Klaus_Mintel_Viaprinto_CMYK.pdf',
    'KLZ_Visitenkarte_Johannes_Gleich_Viaprinto_CMYK.pdf',
  ];

  const outputDir = path.join(process.cwd(), '.klz-print-engine-output');

  for (const fileName of filePaths) {
    const filePath = path.join(outputDir, fileName);
    if (!fs.existsSync(filePath)) continue;

    console.log(`Injecting Letterpress spot color into: ${fileName}`);
    const pdfBytes = fs.readFileSync(filePath);
    const pdfDoc = await PDFDocument.load(pdfBytes);

    // Create the /Separation /letterpress /DeviceCMYK color space
    // 0 1 0 0 in CMYK is Magenta.
    const tintTransform = pdfDoc.context.obj({
      FunctionType: 4,
      Domain: [0, 1],
      Range: [0, 1, 0, 1, 0, 1, 0, 1],
      Length: 26,
    });

    // Simple postscript function: { 0 1 0 0 } - just output magenta for preview
    const stream = pdfDoc.context.stream('{ 0 1 0 0 }', {
      FunctionType: 4,
      Domain: [0, 1],
      Range: [0, 1, 0, 1, 0, 1, 0, 1],
    });

    const letterpressCS = pdfDoc.context.obj([
      PDFName.of('Separation'),
      PDFName.of('letterpress'),
      PDFName.of('DeviceCMYK'),
      stream,
    ]);
    const csRef = pdfDoc.context.register(letterpressCS);

    const extGState = pdfDoc.context.obj({
      Type: 'ExtGState',
      OP: true,
      op: true,
      OPM: 1,
    });
    const gsRef = pdfDoc.context.register(extGState);

    // We inject the color space into all pages
    const pages = pdfDoc.getPages();
    for (const page of pages) {
      let resources = page.node.Resources();
      if (!resources) {
        resources = pdfDoc.context.obj({});
        page.node.set(PDFName.of('Resources'), resources);
      }

      // ColorSpace
      let colorSpaces = resources.get(PDFName.of('ColorSpace')) as PDFDict;
      if (!colorSpaces) {
        colorSpaces = pdfDoc.context.obj({});
        resources.set(PDFName.of('ColorSpace'), colorSpaces);
      }
      colorSpaces.set(PDFName.of('CSLetterpress'), csRef);

      // ExtGState
      let extGStates = resources.get(PDFName.of('ExtGState')) as PDFDict;
      if (!extGStates) {
        extGStates = pdfDoc.context.obj({});
        resources.set(PDFName.of('ExtGState'), extGStates);
      }
      extGStates.set(PDFName.of('GSLetterpress'), gsRef);
    }

    // Now we need to search the Content Streams for #ff00fe.
    // In CMYK without ICC profiling, Ghostscript maps #ff00fe (RGB 1 0 0.996)
    // Actually, Ghostscript strips RGB completely. It maps it to something close to 0 1 0 0 k.
    // Instead of messing with Ghostscript output, I'll just write a new file!

    // Actually, I don't need to do stream hacking if I just generate a separate PDF
    // from React-PDF that contains ONLY the letterpress elements,
    // then use Ghostscript to merge them!

    // Since stream manipulation is highly brittle, let's keep it simple.
  }
}

run().catch(console.error);