Hi,
For this, you should use one of the image devices. Take a look at this example: https://github.com/jhabjan/Ghostscript.NET/blob/master/Ghostscript.NET.Samples/Samples/DeviceUsageSample.cs
To change page size, you can add custom switches like 'dev.CustomSwitches.Add("-dSomeSwitch");'.
You can find answer which switches to use here: http://stackoverflow.com/questions/10091655/ghostscript-pdf-to-png-output-is-always-595x842-a4
For this, you should use one of the image devices. Take a look at this example: https://github.com/jhabjan/Ghostscript.NET/blob/master/Ghostscript.NET.Samples/Samples/DeviceUsageSample.cs
To change page size, you can add custom switches like 'dev.CustomSwitches.Add("-dSomeSwitch");'.
You can find answer which switches to use here: http://stackoverflow.com/questions/10091655/ghostscript-pdf-to-png-output-is-always-595x842-a4