Gmail Invoice PDF Extractor: OpenAI to Google Sheets + Slack

Turn Gmail PDF invoices into structured rows—and Slack alerts

This Gmail Invoice PDF Extractor n8n workflow automatically scans your Gmail inbox for unread emails with PDF invoice attachments, extracts the invoice text, uses OpenAI to structure key fields, saves them to Google Sheets, and posts a concise summary to Slack.

What this workflow does

• Monitors Gmail every minute for unread emails that include a PDF attachment, downloads the attachment, and prepares it for extraction.
• Extracts invoice text from the PDF into a single combined text output.
• Uses OpenAI to extract structured invoice fields from the PDF text, including:
  • vendor
  • invoice number
  • invoice date
  • due date
  • currency
  • total amount
  • tax amount
  • a short summary
• Adds metadata such as the sender email address (email_from) and the current timestamp (received_at).
• Appends one new row per invoice to a selected Google Sheets worksheet (e.g., columns: vendor, invoice_number, invoice_date, due_date, currency, total_amount, tax_amount, summary, email_from, received_at).
• Posts a formatted notification to Slack with the invoice details in a chosen channel (optional—can be disabled).

Use cases

• Accounts teams capturing invoice data from supplier emails without manual copy/paste.
• SaaS operators monitoring recurring billing invoices and receiving instant Slack alerts for new documents.
• Automation engineers standardizing inbound invoice intake pipelines using n8n + OpenAI + Google Sheets.

Technical details

• n8n Gmail Trigger (runs every minute for unread emails with PDF attachments)
• extract from file to convert PDF content into text
• OpenAI to structure invoice fields from extracted text
• Google Sheets integration to append rows to the specified spreadsheet/worksheet
• Slack node to send a concise invoice summary
• Includes setup via OAuth2 for Gmail, Google Sheets, and Slack