PDF is the most widely used file format in daily life for its excellent compatibility with every operating system and device. Except for adding a password, another common way to keep your PDF file safe and secure is to flatten the PDF. Do you know what does “flatten PDF” means and how to do that? This article by SwifDoo PDF will give you an answer.

What Does Flatten PDF Mean

Simply put, if you flatten a PDF, you combine all layers in the PDF into one, making it an image-like PDF. As a result, your PDF file will become non-fillable and non-editable. All the interactive elements such as checkboxes and radio buttons no longer work.

When you flatten a PDF, there will be a slight reduction in the quality of images inside the file. The quality reduction is so small that you cannot detect it with your eyes.

To tell whether a PDF is flattened, you can use a PDF highlighter to check if you can make changes on the page or test the interactive parts.

When Do You Need to Flatten PDF

Multiple layers of PDF documents may cause printing problems. As a result, the files may not be printed as intended. If you flatten a PDF before you print it, you can make sure the final printed result meets your needs.

“Flatten PDF” is an effective way to prevent unwanted modification made to your document. This function is especially useful when it comes to collaborating on PDFs online.

While transferring large files, there is often a size limit, for instance, 25MB for each email. Flattening PDFs can help you reduce the size for of PDF documents.

How to Flatten PDF

To flatten a PDF, you can use SwifDoo PDF, a program that provides a one-stop PDF solution. Simply open your PDF file with this software, tap “Protect > Flatten”, choose where to store the output file, and hit the “Start” button.

You can also flatten PDFs with an online tool. You should first upload your PDF online, choose whether to flatten everything or just form fields, and then download the flattened PDF. An online tool often has a limit on the file size you can process.

Before you flatten a PDF, we suggest you make a copy of the file since the action is irreversible.

Flatten PDF Online for Free without Losing Quality 2023

Flatten PDF Online for Free without Losing Quality 2023

This guide will tell you how to flatten PDF online. You will also learn the advantages and disadvantages of flattening PDF online.


Demi is curious about the technology field and is always passionate to explore new things. She is now working as a copywriter for this website. Demi will introduce many useful tips to improve your workflow.