A PDF can carry more than its pages. Form fields, comments, highlights, stamps and sticky notes sit on separate layers that stay editable and can look different from one reader to the next. Flattening merges those layers into the page. Flatten PDF does this in three strengths, for one file or many, without uploading anything.
Each form field or annotation in a PDF has an appearance: a small drawing of how it should look, such as a box with text, a tick, or a yellow highlight. A reader draws that appearance over the page and keeps the item interactive, so it can be edited, moved or deleted.
Flattening draws those appearances into the page's own content and removes the interactive items. The page looks the same, but there is nothing left to click into. Form fields are removed from the document's form, so readers stop offering them for editing.
Mostly to stop surprises.
The most common reason is a completed form. Unflattened, anyone who opens it can change an answer, and some printers, phone viewers and online previews show the fields empty. Flattened, the answers are just part of the page.
Other reasons: sending a reviewed document where comments and stamps should stay visible but not editable, merging or printing files that include annotations, and making sure a document looks the same in every reader.
Forms and annotations flattens both form fields and annotations such as comments, highlights, stamps, sticky-note icons and drawings. Text stays selectable and searchable, and the file size barely changes. Form fields only locks the answers but leaves comments and highlights editable, which suits a form that still has reviewer notes on it.
Everything into images renders each page, with its fields and annotations, into one picture and builds a new PDF from those pictures. Choose 75 to 300 dpi and JPEG or lossless PNG. It is the most complete flatten, but text can no longer be selected, and files are usually larger.
Keep links clickable is on by default, so web and page links still work after flattening. Interactive media and file attachments are left as they are, because flattening them would only leave a picture of a button.
Fields or comments with no saved appearance, or marked hidden, have nothing to draw, so they are removed and counted in the report. A digitally signed PDF can be flattened and the signature's look is kept, but the signature can no longer be verified, since the file has changed. Keep the signed original if that matters.
Add as many PDFs as you need. Before you start, the list shows each file's page count, form fields and annotations, and flags files that cannot be opened, such as password-protected ones, which need unlocking first.
Press Flatten and the files are processed one after another with the same settings. Each row then reports what was flattened and the size before and after. One file downloads as a PDF; several download together as a ZIP, and any single result can be saved again from its row.
Input: contract-v3.pdf, reviewed by a colleague who added eight comments, two highlights and an Approved stamp, and supplier-form.pdf, a filled form with 24 fields. Drop both in. The list shows contract-v3.pdf with 0 form fields and 11 annotations, and supplier-form.pdf with 24 form fields.
Keep Forms and annotations selected and Keep links clickable ticked, then press Flatten. The contract's comments, highlights and stamp are drawn into its pages; the supplier form's answers become page content and its fields disappear. Both files keep their selectable text and stay close to their original size, and flattened-pdfs.zip holds contract-v3-flattened.pdf and supplier-form-flattened.pdf. If the contract's sticky-note text needed to stay readable, you would flatten it with Form fields only instead, since a flattened note keeps its icon but not its pop-up text.
Start with the lightest mode that does the job. For a filled form you are sending back, Form fields only or Forms and annotations is enough, keeps the file small and keeps the text searchable. Use Everything into images when you need every reader to show exactly the same picture, or when text should not be easy to copy.
Flattening cannot be undone in the output file, so keep the original if you might need to change an answer later. A sensible habit is to archive the editable original and send the flattened copy. All processing happens in your browser tab, and the files are never uploaded, so confidential contracts and personal forms stay on your device.
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