acroform

A high-level PDF form manipulation library using lopdf.

This crate provides a simple API for reading and filling PDF forms (AcroForms). It uses the official lopdf crate for PDF operations.

Features

• Load PDF documents from files or bytes
• List all form fields with their properties
• Fill form fields with typed values
• Save filled PDFs to files or bytes
• Support for text, boolean, choice, and integer field types
• Automatic UTF-16BE encoding for text fields
• Hierarchical field name resolution

Usage

Add this to your Cargo.toml:

[dependencies]
acroform = "0.2.0"

Example

use acroform::{AcroFormDocument, FieldValue};
use std::collections::HashMap;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Load a PDF with form fields
    let mut doc = AcroFormDocument::from_pdf("form.pdf")?;

    // List all fields
    let fields = doc.fields()?;
    for field in &fields {
        println!("Field: {} ({})", field.name, field.field_type);
    }

    // Fill fields
    let mut values = HashMap::new();
    values.insert("name".to_string(), FieldValue::Text("John Doe".to_string()));
    values.insert("age".to_string(), FieldValue::Integer(30));
    values.insert("subscribe".to_string(), FieldValue::Boolean(true));

    // Save filled PDF
    doc.fill_and_save(values, "filled_form.pdf")?;
    
    Ok(())
}

API

AcroFormDocument

The main struct for working with PDF forms.

Methods

• from_pdf(path: impl AsRef<Path>) -> Result<Self> - Load a PDF from a file path
• from_bytes(data: Vec<u8>) -> Result<Self> - Load a PDF from bytes
• fields(&self) -> Result<Vec<FormField>> - Get all form fields
• fill(&mut self, values: HashMap<String, FieldValue>) -> Result<Vec<u8>> - Fill fields and return PDF bytes
• fill_and_save(&mut self, values: HashMap<String, FieldValue>, output: impl AsRef<Path>) -> Result<()> - Fill fields and save to file

FormField

Represents a form field with its properties.

Fields

• name: String - The fully qualified field name (e.g., "parent.child.field")
• field_type: FieldType - The type of the field
• current_value: Option<FieldValue> - The current value
• default_value: Option<FieldValue> - The default value
• flags: u32 - Field flags (bit field)
• tooltip: Option<String> - Tooltip text

FieldValue

Typed values for form fields.

Variants

• Text(String) - Text string
• Boolean(bool) - Boolean value (for checkboxes)
• Choice(String) - Choice value (for radio buttons, list boxes, combo boxes)
• Integer(i32) - Integer value

FieldType

PDF form field types.

Variants

• Text - Text field (/Tx)
• Button - Button field (/Btn) - includes checkboxes, radio buttons, and push buttons
• Choice - Choice field (/Ch) - includes list boxes and combo boxes
• Signature - Signature field (/Sig)
• Unknown(String) - Unknown or custom field type

Implementation Details

String Encoding

Text fields are automatically encoded as UTF-16BE with BOM when filling forms, which ensures proper Unicode support across PDF viewers.

Field Hierarchy

Fields can be organized hierarchically in PDF forms. This library constructs fully qualified field names using dot notation (e.g., "parent.child.field").

Appearance Updates

When filling forms, the library sets the NeedAppearances flag, which tells PDF viewers to regenerate field appearances. This ensures that filled values are properly displayed.

Python Bindings

High-performance Python bindings are available:

pip install acroform

Requires Python 3.12 or later.

import acroform

# Load a PDF form
doc = acroform.AcroFormDocument.from_pdf("form.pdf")

# List all fields
fields = doc.fields()
for field in fields:
    print(f"Field: {field.name} ({field.field_type})")

# Fill fields and save
doc.fill_and_save({"name": "John Doe"}, "filled_form.pdf")

See PYTHON_BINDINGS.md for detailed documentation.

License

MIT

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.