What does flattening a PDF do?

It turns interactive parts of a PDF into ordinary page content. In Form fields mode, each visible field on the chosen pages (text boxes, check boxes, radio buttons, drop-downs, push buttons and signatures) that has a stored appearance is drawn into the page from it, exactly where a reader shows it, and then removed, so there is nothing left to type into or tick. Hidden fields are removed without being drawn, because they were not shown. The page's own text, links and comments are not touched. Raster mode goes further and redraws each chosen page as a single image.

What is the difference between Form fields mode and Raster mode?

Form fields mode changes only the form: text on the page stays selectable, vector drawings stay sharp at any zoom, links still work and comments stay comments. Raster mode redraws each chosen page as one picture at 72, 100, 150, 200 or 300 DPI (lower only for a page too large for a browser canvas, which the report names), with its highlights, shapes, stamps and fields drawn in, so those markups are fixed in place, but the page loses its selectable text, vector graphics and links, and a drawn comment's pop-up note no longer opens. A 792 by 612 point landscape page at 150 DPI becomes a 1650 by 1275 pixel image and is still landscape. Pages you do not choose are left as they are in both modes.

Can a flattened PDF still be edited, or is the information hidden?

It can still be edited, and nothing is hidden. Flattening removes the form, not the information: in Form fields mode the values become text and drawings in the page, which any PDF editor can select, copy or change, and in Raster mode the page is a picture that can be read, painted over or run through OCR. Flattening is not redaction. It also does not remove the values from pages you did not choose, from bookmarks or from the file's properties.

What happens to a digital signature?

It stops validating. A signature covers the exact bytes of the file it was made on, and a flattened copy is a rewritten file, so the report says the signature is now invalid whenever the PDF carries one, even if the signature's own page was not chosen. In Form fields mode the signature's visible appearance is drawn into the page as it was shown; an empty signature field with an appearance is drawn and removed too, so that copy can no longer be signed there. Your original file is not changed.

Why was a field kept and outlined instead of being flattened?

Because it has no appearance that can be drawn faithfully. That happens when a field has no stored appearance at all, when a check box has no picture for the state it is in, or when a text field's stored appearance is blank although the field holds a value. Drawing any of those would make the value disappear, so the field is kept as a working field, listed in the report with its page and outlined on the preview. Raster mode draws such a text field when the PDF asks readers to redraw fields from their values, because the page renderer then draws the value itself. A comment whose icon only a reader's comment layer adds is kept and outlined in Raster mode for the same reason.

Is my PDF uploaded, and are there limits?

Nothing is uploaded. The PDF is read, flattened, previewed and saved in this browser tab with pdf-lib and pdf.js, and no byte of it, its name or its field values goes to analytics. PDFs up to 50 MB and 100 pages are accepted. A PDF that needs a password to open is refused, since there is no password prompt, and so is one encrypted with an owner password, because a flattened copy cannot be written without removing that protection. The only thing remembered between visits is the DPI you last chose.

How do I know the flattened copy came out right?

The copy is parsed again from its own bytes before it is offered, and the number of fields left in it, its pages and each page's size and turn come from that reading, not from what the tool meant to do. If the copy does not have the same pages, it is not offered. The Before and After previews draw the chosen page from the original and from the copy, so a value, a tick or a highlight can be compared by eye.

PDF Flattener

Open a PDF and choose how to flatten it. Form fields mode draws each visible field's stored appearance into the page and removes the field, so the values stay visible as part of the page while its text, links and comments are left as they were. Raster mode redraws the pages you choose as one image each, at the DPI you pick from 72 to 300, with highlights, shapes and fields drawn where they were and each page's size and orientation kept. Before you download, a report says what was drawn, what was removed and what was lost, and Before and After previews show the page both ways. A digital signature is reported invalid, and a field or markup with no appearance to draw is kept and outlined on the preview instead of disappearing. The flattened copy is read back in the tab to count the fields left in it, and the file never leaves your device.

PDFnone open

Its form fields, comments and links are listed here, page by page, with each value.

reportform fields mode

The page appears here before and after flattening.

· or drop one anywhere on the stage

Never uploadedNo accountFlattened in this tabUp to 50 MB and 100 pages

Mode

Form fields

Fields

none yet

Signature

none yet

Pages

none yet

Form fields mode. Each visible field's stored appearance is drawn into its page and the field is removed; the page's text, links and comments stay as they were. Every PDF you open starts here and runs at once when it has fields; Raster mode runs only when you choose it.

Text field and checked boxform fields mode
an example form with a filled-in name and a ticked box
Raster mode at 150 DPI, landscape page with a highlight792 x 612 pt
an example landscape page with text and a yellow highlight
Signed PDF, or a field with no stored appearanceform fields mode
an example with a signature value and a field whose appearance was never stored

Accuracy. On the pages you choose, Form fields mode draws each visible field's stored appearance into the page and removes the field, so what was filled in stays visible, and Raster mode redraws the page as one image at the DPI you pick (lower only for a page too large for a browser canvas), removing its selectable text, vector graphics, links and fields. A field or markup whose appearance cannot be drawn is kept as it was and flagged, and a digital signature stops validating because the file is rewritten. Flattening is not secure redaction and does not stop anyone editing the copy later, and PDFs up to 50 MB and 100 pages are processed in this tab, never uploaded.

Common questions

What does flattening a PDF do?: It turns interactive parts of a PDF into ordinary page content. In Form fields mode, each visible field on the chosen pages (text boxes, check boxes, radio buttons, drop-downs, push buttons and signatures) that has a stored appearance is drawn into the page from it, exactly where a reader shows it, and then removed, so there is nothing left to type into or tick. Hidden fields are removed without being drawn, because they were not shown. The page's own text, links and comments are not touched. Raster mode goes further and redraws each chosen page as a single image.
What is the difference between Form fields mode and Raster mode?: Form fields mode changes only the form: text on the page stays selectable, vector drawings stay sharp at any zoom, links still work and comments stay comments. Raster mode redraws each chosen page as one picture at 72, 100, 150, 200 or 300 DPI (lower only for a page too large for a browser canvas, which the report names), with its highlights, shapes, stamps and fields drawn in, so those markups are fixed in place, but the page loses its selectable text, vector graphics and links, and a drawn comment's pop-up note no longer opens. A 792 by 612 point landscape page at 150 DPI becomes a 1650 by 1275 pixel image and is still landscape. Pages you do not choose are left as they are in both modes.
Can a flattened PDF still be edited, or is the information hidden?: It can still be edited, and nothing is hidden. Flattening removes the form, not the information: in Form fields mode the values become text and drawings in the page, which any PDF editor can select, copy or change, and in Raster mode the page is a picture that can be read, painted over or run through OCR. Flattening is not redaction. It also does not remove the values from pages you did not choose, from bookmarks or from the file's properties.
What happens to a digital signature?: It stops validating. A signature covers the exact bytes of the file it was made on, and a flattened copy is a rewritten file, so the report says the signature is now invalid whenever the PDF carries one, even if the signature's own page was not chosen. In Form fields mode the signature's visible appearance is drawn into the page as it was shown; an empty signature field with an appearance is drawn and removed too, so that copy can no longer be signed there. Your original file is not changed.
Why was a field kept and outlined instead of being flattened?: Because it has no appearance that can be drawn faithfully. That happens when a field has no stored appearance at all, when a check box has no picture for the state it is in, or when a text field's stored appearance is blank although the field holds a value. Drawing any of those would make the value disappear, so the field is kept as a working field, listed in the report with its page and outlined on the preview. Raster mode draws such a text field when the PDF asks readers to redraw fields from their values, because the page renderer then draws the value itself. A comment whose icon only a reader's comment layer adds is kept and outlined in Raster mode for the same reason.
Is my PDF uploaded, and are there limits?: Nothing is uploaded. The PDF is read, flattened, previewed and saved in this browser tab with pdf-lib and pdf.js, and no byte of it, its name or its field values goes to analytics. PDFs up to 50 MB and 100 pages are accepted. A PDF that needs a password to open is refused, since there is no password prompt, and so is one encrypted with an owner password, because a flattened copy cannot be written without removing that protection. The only thing remembered between visits is the DPI you last chose.
How do I know the flattened copy came out right?: The copy is parsed again from its own bytes before it is offered, and the number of fields left in it, its pages and each page's size and turn come from that reading, not from what the tool meant to do. If the copy does not have the same pages, it is not offered. The Before and After previews draw the chosen page from the original and from the copy, so a value, a tick or a highlight can be compared by eye.

On the pages you choose, Form fields mode draws each visible field's stored appearance into the page and removes the field, so what was filled in stays visible, and Raster mode redraws the page as one image at the DPI you pick (lower only for a page too large for a browser canvas), removing its selectable text, vector graphics, links and fields. A field or markup whose appearance cannot be drawn is kept as it was and flagged, and a digital signature stops validating because the file is rewritten. Flattening is not secure redaction and does not stop anyone editing the copy later, and PDFs up to 50 MB and 100 pages are processed in this tab, never uploaded.