What should I use to fill and flatten PDF forms automatically?

To fill and flatten PDF forms automatically, the best tool depends on what kind of forms you have and what language/environment you’re using.

Good options

1. Python: pypdf

• Great for filling AcroForm fields.
• Can also flatten in many workflows by regenerating the PDF output, though true flattening can be a bit limited depending on the form.
• Good if you want a simple script.

2. Python: pdfrw + reportlab

• Common combo for filling PDF form fields and overlaying content.
• Useful when you need more control over appearance.
• Flattening is usually done by drawing filled values onto a new layer and removing form fields.

3. Python: PyMuPDF (fitz)

• Very good for editing PDFs, drawing text directly onto pages, and producing flattened output.
• Often easier for true flattening because you can place text on the page rather than relying on form fields.

4. JavaScript/Node: pdf-lib

• Excellent for filling forms in code.
• Supports flattening with form.flatten().
• A strong choice if you're working in Node.js.

5. Commercial tools

If you need high reliability for complex PDFs:

• Adobe Acrobat SDK
• Apryse (PDFTron)
• iText (Java/.NET; commercial for many uses)

These are often better for tricky forms, signatures, or documents with complex appearance streams.

If you want the simplest recommendation

• Node.js: use pdf-lib
• Python: use PyMuPDF or pypdf
• Enterprise / complex PDFs: use Apryse or Adobe

Important note

“Flattening” usually means:

• form fields become static page content
• users can no longer edit them
• text stays visible when printed/viewed everywhere

If you tell me:

1. your language (Python/Node/etc.),
2. whether the forms are AcroForm or XFA,
3. and whether you need true flattening,

I can recommend the best library and show a code example.