# PDF Form & Signature Studio

> List and fill PDF form fields, and place a visible signature image or typed name on a page. Shows every field of a fillable PDF (name, type, value, options), fills text fields, checkboxes, radio buttons and drop-downs, and optionally flattens the form. It can also stamp a visible signature, from an uploaded PNG/JPG or a typed name in a script font, at an exact position on any page. This is a picture of a signature, not a cryptographic digital signature.

Part of usefulweb.site (https://usefulweb.site/). Results are deterministic calculations from the inputs and the listed assumptions; the API returns exactly what the web page shows.

## Use it
- Human interface: https://pdfformsignaturestudio.usefulweb.site/ (interactive tool at https://pdfformsignaturestudio.usefulweb.site/tool)
- JSON API: POST https://pdfformsignaturestudio.usefulweb.site/api/v1/calculate with a JSON object of inputs (schema: https://pdfformsignaturestudio.usefulweb.site/api/v1/tool)
- OpenAPI: https://pdfformsignaturestudio.usefulweb.site/openapi.json
- MCP (Streamable HTTP): https://pdfformsignaturestudio.usefulweb.site/mcp - tool `pdf_form_signature_studio`

## Inputs
- file (file, required): PDF - Max 100 MB. Processed on our server and deleted; the result can be downloaded for about 2 hours.
- action (select): What to do
- values (table): Field values - Field name exactly as listed. Checkboxes: yes/no. Radio buttons and drop-downs: one of the listed options. Multi-select lists: options separated by ";".
- valuesText (textarea): More values as text - Optional: one "field name = value" per line (useful for long forms).
- flatten (boolean): Flatten the form (values become part of the page and can no longer be edited)
- signatureImage (file): Signature image - PNG with a transparent background works best. A white JPG background is made transparent. Max 5 MB.
- signatureText (text): Or type your name - Rendered in a handwriting-style font when no image is uploaded.
- signatureColor (select): Ink colour (typed name)
- page (integer): Signature page
- x (number): Distance from the left edge - 72 pt = 1 inch = 25.4 mm. An A4 page is 595 × 842 pt, US Letter 612 × 792 pt.
- y (number): Distance from the top edge
- width (number): Signature width - The height follows from the image proportions.
- password (text): PDF password (only if the file is protected) - Used only to open the file for this conversion; it is written to a private temporary file, never to a command line, and deleted with the job.

## Method
- Fields are read with qpdf's JSON view of the AcroForm (/AcroForm /Fields): full name, type (text, checkbox, radio, drop-down, list, signature), current value, options and page. XFA-only forms (dynamic Adobe forms) are not supported.
- Values are written into the field objects (/V, and /AS for checkbox/radio widgets). /NeedAppearances is set to true so viewers redraw the fields, and qpdf --generate-appearances draws text and choice fields so they show up everywhere, including when flattened.
- Checkboxes accept yes/no (or the on-state name), radio buttons and drop-downs one of their options. Read-only fields, unknown names and invalid options are skipped and listed, never guessed.
- Visible signature: the image (or the typed name rendered in a handwriting-style font with ImageMagick) is placed on a transparent overlay page of exactly the target page size at 200 DPI, converted with img2pdf and laid over the page with qpdf --overlay. Positions are in points from the top-left corner.
- This is NOT a cryptographic (digital) signature: it proves nothing about who signed or whether the document was changed. Use a qualified e-signature service when a legally binding electronic signature is required.

## Limits
- A visible signature image is not a digital signature. Existing digital signatures in the PDF become invalid when you fill or stamp it.