How to Flatten a Fillable PDF in Minutes (2025 Guide)

Need your PDF to look the same on every device? Or want to stop others from changing your file? Flattening your PDF is the answer.

It locks everything in place—text, comments, and even signatures—so what you see is exactly what others get.

Not sure what flattening means or when to use it? No worries. We’ll explain what it is, why it matters, and how to flatten a fillable PDF in just a few clicks with Smallpdf.

Quick Steps to Flatten a PDF Fast

1. Open Smallpdf’s Flatten PDF tool.
2. Upload your file from your device or drag and drop it.
3. Choose your mode: Flatten forms only or Flatten all content.
4. Download your flattened PDF, now locked and ready to share or print.

What Does It Mean to Flatten a PDF?

When you flatten a PDF, you combine all interactive elements—like form fields, annotations, and separate layers—into a single, static layer that can’t be edited. This creates a read-only version of your document where everything appears exactly as intended, but nothing can be changed or removed.

Once flattened, a PDF’s content cannot be edited or interacted with, meaning elements like form fields or comments will no longer be clickable or modifiable.

This process is helpful when you want to ensure your document looks consistent on any device or when the PDF is ready for sharing or printing.

Examples of Interactive Elements in PDFs

• Form Fields (fillable sections)
• Annotations (highlighting, comments)
• Images (that can be moved or edited)
• Signatures (especially in fillable contracts)

Flattening creates a file that replaces these editable components with static content. A flattened document is easier to view, share, or print without concerns about unintended changes in its structure or content.

How to Flatten a PDF Online

Flattening a PDF is simpler than you might think, especially with Smallpdf. You don’t need special software or technical know-how. Here’s how you can do it:

1. Go to our tool: Head over to Flatten PDF.
2. Upload your PDF: Drag and drop your file into the upload area, or click to select it from your device.
3. Choose your flattening mode: Select “Flatten forms only” to lock form fields, or “Flatten all content” to make the entire PDF non-editable.
4. Download your flattened PDF: Once it’s ready, hit “Download” to save the final version to your device. The form fields, comments, and other layers are now locked in place.

Why Flatten a PDF?

Flattening serves multiple purposes whether your goal is to secure sensitive information, simplify sharing, or ensure formatting consistency. Here’s why it’s useful:

• Ensure consistent printing: It guarantees your document looks the same, no matter which device or platform is used to open the PDF.
• Prevent unauthorized edits: Stop others from altering interactive elements like form fields or annotations. A flattened PDF keeps your content secure and intact.
• Preserve form submissions: Lock in completed form data so responses can’t be changed after submission.
• Share final versions securely: Perfect for legal contracts, reports, or private documents where data integrity matters.
• Improve compatibility across viewers: Since interactive elements are converted into a simple layer, your file becomes universally viewable—even on PDF readers with limited functionality.

Still wondering, “Why do you flatten a PDF?” or “What is the best way to flatten PDFs?” Here are specific scenarios where flattening makes a difference:

• Legal Documents: Lock legal contracts to secure client signatures and annotations.
• Business Reports: Prevent unintentional edits in finalized presentations or reports.
• Graphic Design Projects: Ensure formatting remains consistent when sharing designs.
• Educational Materials: Teachers often flatten answer keys or solutions to prevent tampering.

If you want to flatten multiple PDFs simultaneously, Smallpdf provides tools to handle bulk processing.

If you’re asking yourself, “Should I flatten a PDF before sharing?” or “When do you need a flattened PDF?”—the answer is simple. Flatten whenever you want the document to remain uneditable and consistent.

Start Flattening Your PDFs Today

Whether you’re sharing contracts, preparing final reports, or sending forms, Smallpdf makes it easy to flatten PDFs and use any of our 30+ tools in one place.

Need more flexibility? Try Pro free for 7 days to unlock unlimited use.

FAQs About Flattening PDFs

Does flattening a PDF remove signatures?

It keeps the appearance of your signature, but it turns it into a static image. You can’t move it, delete it, or click it after flattening. If you need a legally binding e-signature, complete the signing step before flattening.

Can I flatten a PDF on my phone?

Yes. Smallpdf works in your mobile browser. Open the Flatten PDF tool, upload your file, choose your mode, and download the final version. No app is required.

Does flattening change file size?

It can. Flattening forms only usually keeps the size similar. Flattening all content may increase or slightly reduce the file size because every page becomes a single layer. This is normal and depends on images and layout.

What’s the difference between flattening and printing to PDF?

Printing to PDF also creates a static version, but it can remove bookmarks, links, tags, and accessibility structure. Smallpdf’s flattening keeps the visual layout intact while preserving more of the document’s original structure.

Can I reverse the flattening process?

No. Flattening is permanent. Make sure you save or keep an editable copy before flattening.

Will flattening help with printing issues?

Often, yes. If a PDF keeps losing form fields, hides highlights, or prints differently on different devices, flattening can solve the problem by locking everything into one layer.

Why does my viewer still show “Fill & Sign” options after flattening?

Some PDF viewers always display editing tools. This doesn’t mean your document is still editable. Check whether fields can actually be clicked or changed. If they can’t, the PDF is already flattened.

Does flattening remove hidden layers?

Yes. Flattening merges all layers into one. Anything that isn’t part of the visible page won’t remain as a separate layer afterward.