Paint.NET only works with 8-bits per color channel. No more, no less. Other color depths are supported when saving or loading, but when it's in memory it's always 8-bits per color component (32-bit RGBA). Even a 1-bit monochrome TIFF from a fax machine gets expanded to 32-bits when opened (which is why you see people asking, "I opened a 800KB TIFF and it said out of memory whyyyyyyyy").
You won't be able to use Paint.NET for this purpose.