Flatten a PDF

What does flattening a PDF do?

Flattening merges annotations and form fields into the page content, so what used to be separate, editable objects becomes a fixed part of the page. In the PDF specification, ISO 32000-2, fields and annotations live in their own list beside the page content, and each viewer decides how to draw them. After flattening there is only one layer, which every viewer and printer shows identically.

The visible result does not change: filled answers, highlights, drawings and stamps stay exactly where they were. What changes is that a recipient can no longer click into a field, retype a figure, move a stamp or delete a comment in a normal PDF reader. The table shows what happens to each kind of element with the default option.

When should I flatten a PDF?

Flatten a document when it is finished and should look identical for everyone who opens it. Typical moments are after filling and signing an application, before sending a quote or contract whose fields someone might change, when archiving reviewed drafts with their comments visible, and before printing forms that some printers or apps render with empty fields.

Flattening can also fix upload portals that reject PDFs with active form fields, and it prevents a recipient from quietly changing a figure in a filled quote or order form before passing it on. Do not flatten a form that will be read by software, such as an online application system that extracts field values, because flattening deletes the fields that the system reads.

Which flattening option should I choose?

Choose the lightest option that solves your problem, which for most people is the default, Forms and annotations. It locks answers and markup while keeping text sharp, searchable and small. The image option is a last resort for files that must not contain selectable text at all, and it offers three quality levels: Small at 110 dpi, Standard at 150 dpi and High at 220 dpi.

• Forms and annotations: field values, comments, highlights, drawings and stamps are drawn into the page. Text stays sharp and searchable.
• Form fields only: answers are locked while review comments stay editable for the next reader.
• Everything as images: each page is rendered to a picture with pdf.js. Nothing can be selected or edited, but the file is usually larger and no longer accessible to screen readers.

How does the tool flatten fields and annotations?

Form fields are flattened by regenerating their appearances from the current values and merging those appearances into the page content. Other annotations are painted from their own appearance streams at their exact position, respecting transparency, and are then removed from the page's annotation list. Before you start, the tool shows how many fields and annotations were found, by type, so you know what will change.

Flattening cannot be undone in the saved file, so keep the editable original. Image flattening of long documents takes time and memory, especially on phones, because every page is rendered one by one. Afterwards, Compress PDF can shrink image-based output, and Protect PDF adds a password against further changes.

Does flattening remove hidden or sensitive information?

No, flattening fixes content in place and does not delete what is on or under the page. A flattened comment or highlight is still visible, and text covered by a flattened box can remain in the file underneath it, where it can be found by search or copy and paste. Flattening is about consistency and casual tamper resistance, not confidentiality.

If a document contains personal data or confidential figures that the recipient must not see, remove them with Redact PDF first, then flatten. Document properties such as author and title are untouched by flattening too, and Remove PDF Metadata clears those. A typical safe order before publishing is to fill in the form with Fill PDF Form, sign, redact, flatten and finally protect the file.