How to Compress a PDF Without Uploading It
A browser-local PDF size reducer can decrease PDF size without an upload, but this workflow rasterizes pages and may remove selectable text, links, forms, and document structure.
Read guide →Flatten PDF
Rebuild a PDF as page images so annotations, form fields, and layers render identically in every viewer.
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Reviewed 2026-08-15
Free Flatten PDF – how it works
Flattening renders each page to a raster image and assembles those images into a new PDF. Everything that was a separate interactive or layered object, including form fields, comments, annotations, and optional content groups, becomes part of a single flat picture of the page.
The reason to do this is predictability. A form field or annotation is drawn by the viewer, and viewers disagree. A field that shows a value in Acrobat can appear empty in a browser preview or print blank. Once the page is an image, every reader shows the same thing because there is nothing left to interpret.
Two settings control the result. Resolution runs from 72 to 240 DPI, and JPEG quality from 50 to 100. Both push in the same direction: higher values look better and produce a bigger file. If you only need to lock down filled form values and want to keep the text layer, use Flatten PDF Forms instead, which flattens the fields without rasterising the pages.
How to use Flatten PDF online
- Add the PDF. Drop in the document that is rendering inconsistently or that you want to make non-editable.
- Set resolution and quality. Start at 150 DPI and 90 percent quality. Move to 240 DPI for print or fine detail, and drop toward 100 DPI when file size matters more than crispness.
- Flatten and compare. Download the result and open it alongside the original. Confirm that annotations and filled fields appear where they should and that the text is still legible at your chosen resolution.
When to use it
- Lock a completed form so the values cannot be edited or accidentally cleared.
- Make sure comments and stamps print rather than being skipped.
- Produce a document that looks the same in every reader before sending it for signature.
- Collapse layered artwork into a single flat page for a print shop.
Known limitations
- Text becomes part of an image, so the document is no longer searchable or selectable and screen readers cannot read it.
- File size usually increases, sometimes substantially, because page images replace compact text and vector instructions.
- Flattening cannot be undone. Keep the original if you might need the interactive version again.
Frequently asked questions
What does flattening a PDF actually do?
It renders each page to an image and builds a new PDF from those images. Form fields, annotations, and layers stop being separate objects and become part of the flat page, so no viewer has to decide how to draw them.
Will the text still be searchable?
No. Rasterising removes the text layer. If you need searchable text and only want to lock form values, Flatten PDF Forms keeps the document structure and flattens just the fields.
Is my PDF uploaded anywhere?
No. The document is processed by WebAssembly and JavaScript running inside the page, so the bytes never leave your device. There is no upload step and nothing to delete afterwards.
Why did my file get bigger?
Because a page of text stored as instructions and font references is far more compact than a photograph of that same page. Lowering the DPI or the JPEG quality brings the size back down.
Does flattening make a document secure?
It makes the content non-editable in ordinary readers, which is different from secure. Metadata survives flattening, and anyone can still copy the images. For confidentiality use Redact PDF and Password Protect PDF.
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