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Flattening turns things that sit on top of a page into part of the page itself. A filled form stops being fillable and becomes a document that reads the same everywhere; a highlight stops being an annotation a reader can drag away and becomes ink. The values and marks are drawn into the page content, and the field and annotation objects are then removed.

Use it before you send a completed form back, so the recipient cannot alter what you entered and no reader can clear the fields by accident. It is also the fix for a form that looks filled on screen and prints blank, and for a marked-up draft you want to circulate with the comments visible but no longer editable.

วิธีทำงาน

1. Drop the PDF onto this page.
2. Leave Flatten form fields on to make the filled values permanent, and Flatten annotations on to burn in highlights, notes, stamps and drawings.
3. Turn one of them off to keep the other: flattening only the annotations leaves the form fillable, and flattening only the form leaves the comments editable.
4. Check the advanced options if you want unfilled fields to stay visible as empty boxes, or the drawing font embedded so the result renders identically elsewhere.
5. Press Flatten. The result reports how many fields and how many annotations were burned in.

There is one failure this tool is built around, and most flatteners fall into it. A form whose /NeedAppearances flag is set carries no drawn appearance for its fields - the reader is expected to render the contents itself from the raw values. Flatten such a file naively and every filled box comes out empty, silently, with the typed data gone. Here the appearances are generated first and then flattened, which is why your entries survive, and any field that could not be drawn is reported rather than quietly dropped.

Links are never flattened, and that is deliberate. A link annotation has no ink of its own - it is an invisible rectangle that responds to a click - so burning it into the page would destroy a working hyperlink and draw nothing in its place. Pop-up windows are skipped for the same reason, and annotations marked hidden are left alone since they were never meant to be seen.

Flattening is one-way. The values are now marks on the page and there is no field left holding them, so no reader can extract, edit or clear them again. Keep the fillable original if you might need to correct an entry, and treat the flattened file as the copy you send rather than the copy you keep.

This is not a digital signature and does not stand in for one. Flattening makes a document harder to edit casually, but the page content is still ordinary PDF an editor can change. If you need evidence that a document has not been altered, sign it; if you need to stop people extracting or editing it, Protect PDF adds the restrictions. Flattening an already-signed document invalidates the signature.

The work happens with pdf-lib in a Web Worker on your device. A completed form usually contains exactly the details you would least like to post to a stranger's server - name, address, account number - and this one never leaves your browser.