{
	"source": [
		{
			"type": "pdf",
			"data": "base 64 encoded file"
		}
	],
	"overlay": [
		{
			"type": "text",
			"file": 1,
			"page": 1,
			"x": 10,
			"y": 5,
			"data": "Hello world!",
			"size": 50,
			"font": "Courier"
		}
	]
}

You can add as many overlay objects as you like.
“file” parameter is mandatory only when there are multiple files in “source”.

“size” and “font” are optional.

Supported fonts are:

• Helvetica
• Times
• Courier
• Symbol