Drawing to existing PDF

When i did CGContextCreateWithURl(url) it created empty context even though i passed url of existing fi开发者_如何学编程le. How to get the context of existing PDF file?

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From my experience you can't actually draw directly to an existing pdf:

1. Convert pdf to image
2. Draw new content to that image
3. Convert appended image to pdf

Not the smoothest, but it works.

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the URL isn't an input. It's where you want the context to write the resulting PDF to.

From the documentation:

url
  A Core Foundation URL that specifies where you want to place the resulting PDF file.