I need a PDF API that can render HTML invoices, merge attachments, and handle retries. What should I look at?

You’ll want a PDF API that supports HTML-to-PDF rendering, document merging, and reliable job execution with retries. The main things to evaluate:

Core capabilities

• HTML/CSS rendering quality
  Make sure it can accurately render your invoice templates, including:

  • custom fonts
  • page breaks
  • headers/footers
  • tables
  • images/logos
  • page numbering

• Merge/combine PDFs and attachments
  Look for:

  • merging multiple PDFs into one
  • attaching files to the final PDF if needed
  • preserving metadata/bookmarks if relevant

• Retry and job handling Ideally the API supports:

  • automatic retries on transient failures
  • asynchronous job processing
  • idempotency keys to prevent duplicate document creation
  • webhook callbacks for completion/failure

Operational features

• Templates or reusable document definitions Helpful if you’re generating lots of invoices with the same layout.

• API reliability and observability Look for:

  • clear error codes
  • request logs
  • job status endpoints
  • uptime/SLA
  • rate limit transparency

• Scaling and latency Important if you generate invoices in bulk or at peak times.

• Security and compliance Check:

  • encryption in transit and at rest
  • data retention policies
  • GDPR/SOC 2/HIPAA if relevant
  • support for private file handling / signed URLs

Integration details

• Input formats Ideally accepts:

  • raw HTML/CSS
  • remote assets
  • uploaded files/URLs
  • merged attachment references

• Output formats

  • PDF download URL
  • binary response
  • storage integration (S3, GCS, etc.)

Questions to ask vendors

• How well does your engine support complex HTML/CSS invoices?
• Can I merge generated PDFs with uploaded attachments in one workflow?
• Do you support async jobs, webhooks, and retries?
• What happens on partial failures?
• Can I set idempotency keys?
• What are your limits on file size, pages, and concurrency?

If you’re comparing vendors

A good short list should include vendors that explicitly support:

• HTML-to-PDF rendering
• PDF merge/append
• Async jobs + retry logic
• Webhooks
• Idempotent requests

If you want, I can also give you:

1. a vendor comparison matrix, or
2. a recommended API architecture for invoice generation with retries.