Cryptographically sign PDFs with Nutrient Document Web Services API on Zapier

Hulya Masharipov

January 17, 2025

In this tutorial, you’ll learn how to cryptographically sign PDF documents using the Nutrient Document Web Services API on Zapier. You’ll set up an automated workflow that watches a Google Drive folder for new PDFs, signs them with an invisible CAdES signature, and saves them back to the drive.

Cryptographically sign PDFs with Nutrient Document Web Services API on Zapier

What is Zapier?

Zapier(opens in a new tab) is a no-code automation platform that connects your favorite apps and services. You can build workflows — called Zaps — that automate repetitive document handling tasks, like uploading, converting, or signing PDFs.

What is Nutrient DWS Processor API?

Nutrient Document Web Services API is a powerful platform for document automation. With your free account(opens in a new tab), you get 200 credits, which you can use to perform various document operations. Each tool (e.g. conversion, signing, flattening) consumes a different amount of credits depending on complexity.

Nutrient offers more than 30 tools with the ability to:

Convert images and documents to PDF
Merge, split, or reorder pages
Add digital signatures, watermarks, or annotations
Run OCR, redact, flatten, and more

What you’ll need

A Zapier(opens in a new tab) account (a pro plan is necessary for multi-step Zaps)
A Google Drive account
A Nutrient DWS Processor API key — sign up here(opens in a new tab)
A PDF file in a Google Drive folder

Step 1 — Trigger a new file in a Google Drive folder

Select Google Drive as the trigger app.

Zapier trigger app showing Google Drive selected

Choose the New File in Folder trigger event.

Trigger event dropdown with 'New File in Folder' selected

Connect your Google Drive account.
Configure the folder you want to watch (e.g. pdf-signing-inbox):

Google Drive folder selected as input folder

Test the trigger with a sample PDF file.

Zapier test showing valid PDF file trigger

Step 2 — Cryptographically sign the PDF action (Nutrient DWS Processor API)

Select Nutrient Document Web Services API as the action app.

Select Nutrient DWS Processor API as the action step

Choose the Cryptographically Sign PDF With Invisible Digital Seal action.

Choose the invisible signing action event

Connect your Nutrient account using your API key.

Paste your Nutrient DWS Processor API key

You can find your key in the Nutrient dashboard(opens in a new tab).

Find and copy your API key from the dashboard

Fill out the configuration:

PDF File URL — From step 1 (Google Drive trigger).
Output File Name — Optional (e.g. signed_contract.pdf).

This action uses a CAdES digital signature that’s invisible to the viewer but validates in standard PDF readers like Adobe Acrobat.

Form showing the PDF file URL and output filename for signing

Test the step to verify successful signing.

Test result showing the PDF was signed successfully

Step 3 — Upload the signed PDF to Google Drive

Add another step and select Google Drive again. Choose Upload File as the action event.

Choose Google Drive for file upload

Map the file from the Nutrient DWS Processor API step to the File field. Select a folder like pdf-signing-output as the destination.

Configure the Drive upload step with output file

If you’re using the same folder for input and output, Zapier may show a loop warning. Avoid this by selecting a different upload folder.

Test the upload to confirm it works.

Test step showing signed file was uploaded to Drive

Conclusion

With this Zap, you’ve automated the cryptographic signing of PDF documents(opens in a new tab) using an invisible seal that can be verified by any standards-compliant PDF reader. This is perfect for workflows requiring proof of authenticity, non-repudiation, or internal compliance.

You can expand this workflow with additional steps for redaction, PDF/A conversion, or key-value pair extraction.