What's free
25,000 conversions/month (Engine 1 & 2) plus 2,500 Engine 3 conversions/month; max 1 MB file, PDFs up to 3 pages
Rate limits
500 requests per day per IP address
The catch
Free searchable-PDF output carries a watermark (raw text extraction is unrestricted); the free key needs only an email, no card. Commercial use permitted.