Resize existing pages?

[Hopding]

Can pdf-lib be used to open an existing PDF document and resize the width and/or height of some of its pages?

[Hopding]

Yes. However, this requires a few custom functions to be written. I've created an example script to demonstrate how this can be done. Here's the high level idea:

// Load the original PDF file
const pdfDoc = PDFDocumentFactory.load(originalPdfBytes);

// Get the first page in the PDF
const pages = pdfDoc.getPages();
const page = pages[0];

// Get the width and height of the page
const { width, height } = getPageDimensions(page);

// Increase the width and height of the page by 200 points.
// Note that this adds 200 points of whitespace to the top of the page,
// and 200 points of whitespace to the right of the page.
setPageDimensions(page, { width: width + 200, height: height + 200 });

// Translate/slide the page's contents to the top right corner of the page,
// (up 200 points and right 200 points) to make use of the new whitespace
// created in the previous step. 
translatePageContents(pdfDoc, page, { x: 200, y: 200 });

// Serialize the modified document
const pdfBytes = PDFDocumentWriter.saveToBytes(pdfDoc);

And here are the custom functions referred to in the above snippet:

const getPageMediabox = page => {
  let mediaBox;

  // Check for MediaBox on the page itself
  const hasMediaBox = !!page.getMaybe('MediaBox');
  if (hasMediaBox) {
    mediaBox = page.index.lookup(page.get('MediaBox'));
  }

  // Check for MediaBox on each parent node
  page.Parent.ascend(parent => {
    const parentHasMediaBox = !!parent.getMaybe('MediaBox');
    if (!mediaBox && parentHasMediaBox) {
      mediaBox = parent.index.lookup(parent.get('MediaBox'));
    }
  }, true);

  // This should never happen in valid PDF files
  if (!mediaBox) throw new Error('Page Tree is missing MediaBox');

  return mediaBox;
};

const getPageDimensions = page => {
  const mediaBox = getPageMediabox(page);
  return { width: mediaBox.array[2].number, height: mediaBox.array[3].number };
};

const setPageDimensions = (page, dims) => {
  const originalMediaBox = getPageMediabox(page);
  const newMediaBox = originalMediaBox.clone();
  newMediaBox.array[2] = PDFNumber.fromNumber(dims.width);
  newMediaBox.array[3] = PDFNumber.fromNumber(dims.height);
  page.set('MediaBox', newMediaBox);
};

const translatePageContents = (pdfDoc, page, shiftAmounts) => {
  const contentsRef = page.getMaybe('Contents');
  let contents = pdfDoc.index.lookupMaybe(page.getMaybe('Contents'));

  if (!contents) {
    contents = PDFArray.fromArray([], page.index);
    page.set('Contents', contents);
  } else if (contents instanceof PDFRawStream) {
    contents = PDFArray.fromArray([contentsRef], page.index);
    page.set('Contents', contents);
  } else if (!(contents instanceof PDFArray)) {
    const type = contents.constructor.name;
    throw new TypeError(`Unknown page.Contents type: ${type}`);
  }

  const startWrapperStream = pdfDoc.createContentStream(
    pushGraphicsState(),
    translate(shiftAmounts.x, shiftAmounts.y),
  );
  const endWrapperStream = pdfDoc.createContentStream(popGraphicsState());

  const startWrapperStreamRef = pdfDoc.register(startWrapperStream);
  const endWrapperStreamRef = pdfDoc.register(endWrapperStream);

  contents.array.unshift(startWrapperStreamRef);
  contents.array.push(endWrapperStreamRef);
};

Here's a zip file containing the complete working script: pdf-lib_page-resizing.zip. To execute it, just download the zip file and run the following:

unzip pdf-lib_page-resizing.zip
cd pdf-lib_page-resizing
yarn install # or npm install
node index.js

Here's the input and output files for the script:

• Input: original.pdf
• Output: modified.pdf

[vegarringdal]

@Hopding
Almost similar tread, so figured I could ask here.
Will this be able to scale pages up or down with all content/annotations?

Need to set a multipage pdfs to be just A4 and A3 sizes.
So anything below A4 needs to be scaled up to A4.
Between A4 and A3 to A4 and above A3 down to A3.

Using print to PDF atm, but I really want to try and automated this,
Atm this lib looks most promising. And it beeing made with typescript only is really impressive.

[sendrel-lambdas]

Works perfectly when increasing the size of the pdf. How can I modify this function so I can decrease the size of the pdf? What happens is that the pdf size decreases but it content doesn't so some of its contents are cut off.

Is it possible?

Thanks.

[vegarringdal]

@sendrel-lambdas
#692

[sendrel-lambdas]

Thanks! Managed to modify it to my liking.

[creativityjuice]

Here is an update of this code for a more recent version of pdf-lib (v1.17.0). I hope it might help as it would have saved me some times. It's made to convert a PDF to A4 or US Letter format, but you can easily change it to resize to any format. I use the scale method when the new ratio of the page is similar to the old one. When it's not the case, I used setSize + scaleContent + translateContent.
My code doesn't deal with annotation and might fail for PDF with different boxes sizes (mediaBox, cropBox, trimBox, ...)

const pageSizes = {
    a4: {
        width: 594.96,
        height: 841.92,
    },
    letter: {
        width: 612,
        height: 792,
    },
};
const resizeToPageFormat = async (snapshot: Uint8Array, paper_format: PaperFormat): Promise<Uint8Array> => {
    // Load the original PDF file
    const pdfDoc = await PDFDocument.load(snapshot, {
        parseSpeed: ParseSpeeds.Fastest,
    });

    const new_size = pageSizes[paper_format || 'a4'];
    const new_size_ratio = Math.round((new_size.width / new_size.height) * 100);

    // Get the first page in the PDF
    const pages = pdfDoc.getPages();

    pages.forEach(page => {
        const { width, height } = page.getMediaBox();
        const size_ratio = Math.round((width / height) * 100);
        // If ratio of original and new format are too different we can not simply scale (more that 1%)
        if (Math.abs(new_size_ratio - size_ratio) > 1) {
            // Change page size
            page.setSize(new_size.width, new_size.height);
            const scale_content = Math.min(new_size.width / width, new_size.height / height);
            // Scale content
            page.scaleContent(scale_content, scale_content);
            const scaled_diff = {
                width: Math.round(new_size.width - scale_content * width),
                height: Math.round(new_size.height - scale_content * height),
            };
            // Center content in new page format
            page.translateContent(Math.round(scaled_diff.width / 2), Math.round(scaled_diff.height / 2));
        } else {
            page.scale(new_size.width / width, new_size.height / height);
        }
    });

    // Serialize the modified document
    return pdfDoc.save();
};

[ll-BSN-ll]

How do I need to alter the code so dat is just set my trimbox to a round number, for example from 411.998 mm to 412.00 mm or from 412.001 to 412.00 mm ?

[ajq47]

Hi! How do you install this exact same node-modules package in this custom code? I think this package is different from

npm install pdf-lib

[ajq47]

Hi @Hopding , I am having an issue with some PDF uploaded here. Looks like some of them are not working on some PDFs. I noticed if it is trimmed, this code doesn't work