用于php curl的-F选项的文件传输

I must 'translate' this curl request :

curl    
-X POST    
-H "Authorization: Bearer YOUR_ACCESS_TOKEN"    
-F "recipients[0][name]=John"    
-F "recipients[0][email]=john.doe@gmail.com"    
-F "files[0]=@/path/to/the/pdf/document.pdf"    
https://api.sandbox.signaturit.com/v3/signatures.json

Into a PHP curl request. The problem is the file, I don't find how to do that in php curl request. Can you help me please ?