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signer

signer is an R package that lets you digitally sign PDF documents and verify digital signatures in PDFs. It uses external tools like BatchPDFSignPortable.jar for signing and pdfsig (part of the Poppler library) for verifying signatures.

Installation

You can install the package directly from GitHub:

# Install the package directly from GitHub
devtools::install_github("StrategicProjects/signer")

Features

This package provides two main functionalities:

1. sign_pdf()

The sign_pdf() function allows you to digitally sign a PDF document using the BatchPDFSignPortable.jar file. The signature can include custom text, and you can control the positioning of the signature in the document.

Usage Example: 

sign_pdf(
  pdf_file = "input.pdf",
  output_file = "signed_output.pdf",
  keystore_path = "keystore.p12",
  keystore_password = "password",
  signtext = "Document digitally signed by CastLab",
  validate_link = "http://castlab.org/validate",
  translate = TRUE
)

Parameters:

  • pdf_file: Path to the input PDF file.
  • output_file: Path where the signed PDF will be saved.
  • fs, rh, rw, rx, ry: Font size, height, width, and signature coordinates.
  • page: Page number where the signature will be placed.
  • signtext: Custom text to include in the signature.
  • validate_link: Optional link for validating the signed document.
  • keystore_path: Path to the .p12 file containing the key and certificate.
  • keystore_password: Password for the .p12 file.
  • translate: If TRUE, the signature text will be in Portuguese; otherwise, it will be in English (default).

2. verify_pdf_signature()

The verify_pdf_signature() function checks the digital signatures in a PDF using the pdfsig command. You can also choose to translate the output to Portuguese.

Usage Example: 

result <- verify_pdf_signature("signed_document.pdf", translate = TRUE)
print(result)

Parameters:

  • pdf_file: Path to the PDF file to be verified.
  • translate: If TRUE, translates the output to Portuguese; otherwise, the result is in English.

Dependencies

This package is supported only on Linux and macOS. It requires the following external tools:

  • Java: Required to run BatchPDFSignPortable.jar for signing PDFs.
  • Poppler: To verify signatures using pdfsig, Poppler must be installed on the system. pdfsig is part of the Poppler library (https://poppler.freedesktop.org/).

Installing Poppler on Linux: 

sudo apt-get install poppler-utils

Installing Poppler on macOS (via Homebrew): 

brew install poppler

Generating a Certificate using Command Line

You can also generate a digital certificate from the command line using OpenSSL. Here are the steps:

Generate a private key: 

openssl genrsa -aes128 -out private_key.key 2048

Create a Certificate Signing Request (CSR): 

openssl req -new -days 365 -key private_key.key -out request.csr

Generate a self-signed certificate: 

openssl x509 -in request.csr -out certificate.crt -req -signkey private_key.key -days 365

Export the certificate to PKCS#12 format: 

openssl pkcs12 -export -out certificate.pfx -inkey private_key.key -in certificate.crt

Credits

This package uses two external tools for signing and verifying PDF documents:

  1. BatchPDFSignPortable.jar: Developed by Josep Marxuach (https://github.com/jmarxuach/BatchPDFSign), BatchPDFSign is a Java utility for signing PDF documents.
  2. pdfsig: Part of the Poppler library, pdfsig is a command-line tool used to verify signatures in PDF documents. The Poppler project is maintained by the Poppler developer community (https://poppler.freedesktop.org/).

License

This package is distributed under the GPL-3 license. See the LICENSE file for more information.