cURL example
curl -X POST https://itextmaster.com/api/external/pdf-tools/merge-pdf \
-H 'x-api-key: YOUR_API_KEY' \
-F 'file=@first.pdf;type=application/pdf' \
-F 'file=@second.pdf;type=application/pdf' \
-F 'options={}' \
--output merged.pdf