How to Flatten a PDF

What is flattening a PDF? If you’ve ever wondered what choosing the “Flattened PDF” export option does to a PDF file, you’re not alone.

In fact, a Google search for “What is flattening a PDF?” comes up with over 20 million results! Here’s what it means to flatten a document and how to do it in PDFpen.

What is flattening a PDF?

When you flatten a PDF, you merge previously separated contents of your document into one. Flattening a PDF makes it so that:

  • Interactive elements in PDF forms such as checkboxes, text boxes, radio buttons, drop-down lists are no longer fillable.
  • Annotations become “native text”.
  • Multiple layers of text, images, page numbers, and header styles become one single layer.

Why flatten PDFs

Document creators flatten their PDF files for different reasons:

1. To “lock” fillable form fields

The article “The Hidden, but Fixable Danger with PDFs” describes the following hypothetical situation:

You enter your banking details in a fillable PDF form in order to receive a sum of money. Unfortunately, the form falls in the wrong hands. Because it’s still fillable, the person is able to change the information so that the money gets wired to them instead.

The article suggests flattening filled-out PDF forms to prevent this type of scam. (Note: This step alone isn’t enough to secure your document, but it’s one layer of protection worth adding.)

2. To get all the visual elements in print

PDFs generated from Adobe InDesign or Adobe Photoshop can contain multiple layers. Flattening them ensures you get all the visual elements on print. Self-publishing ebook company Lulu asks writers to send their books as flattened PDFs for this reason.

Printed book after sending a flattened PDF
Photo by Jonas Jacobsson on Unsplash

3. To improve the usability of a PDF

It isn’t just physical objects that deteriorate with time. PDFs also show signs of wear and tear. An overly used PDF eventually becomes off-spec, causing PDF applications to crash or freeze.

Flattening prevents this. “It streamlines the document to basic PDF specifications so that odd things don’t happen in the future,” says PDFpen product manager Angel Vu.

Flattened PDFs are also faster to render.

4. To make annotations readable in all PDF readers

Some PDF applications may not display certain types of annotations accurately. When you flatten a PDF, you embed the annotations in it, ensuring that they are readable by all PDF readers.

How to flatten a PDF in PDFpen

There are two ways to flatten a PDF using PDFpen:

  1. Choosing File > Print as PDF
  2. Choosing File > Export: Flattened PDF

How to remove flattening in a PDF

A common misconception is that once flattened, a PDF can no longer be edited. The truth is that you can still mark up and select objects in a flattened PDF, including bitmap images such as signatures, provided you have a PDF editor such as PDFpen.

With PDFpen, you can edit electronically-generated PDFs directly or perform optical character recognition (OCR) on scanned files to make their contents editable.

A note about images in flattened PDFs

If you are worried about the possibility of your signature being altered, don’t add an image of your signature to the PDF.

Instead, use the Scribble tool to sign, then flatten the PDF. Because a scribbled signature is an annotation, not an image, it will merge with other contents forming a single layer in the flattened PDF.

Use PDFpen to flatten and edit PDFs

Use PDFpen to flatten PDFs or to edit flattened PDFs.

If you upgrade to PDFpenPro, you get even more features, including the ability to make flattened PDF forms fillable.

Download a 30-day free trial.