When Separation color space with "name" set as None it is falling back to an "alternateSpace" (color space) instead.

From the Pdf specification:
A Separation color space is defined as follows:
[ /Separation name alternateSpace tintTransform ]

Observed:

The None value is ignored and the color space fallbacks to the Lab color space.

When importing a document containing an EI keyword not followed by space or return an exception is thrown: EndOfStreamException: 'Attempted to read past the end of the stream.'

When importing a PDF document and parsing a name start character followed by a dictionary end one an exception is thrown: System.InvalidOperationException: 'Stack empty.'

With the current implementation, the permissions are ignored on import.

As a side note, there is an option to set permissions on export: UserAccessPermissions.

Importing a document containing an EI keyword within the image stream leads to an endless loop and the document is not imported successfully.

Setting a filter on a mask results in an invalid file when exporting. 

Workaround: Set the filer like this:

PdfFormatProvider provider = new PdfFormatProvider();
provider.ExportSettings.ImageCompression = new ImageFilterTypes[] { ImageFilterTypes.FlateDecode };