pdm_kit or pdm_kit_txt utility in r11.2 does not support embedded images. It only supports attachments and the attachment files need to be copied manually from one server to another server.
However, r12.1 supports this out of the box using the new knowledge import/export tools. You could use the knowledge import/export tools to export knowledge with its embedded images from r12.1 to a logical XML format and then to import that XML to another r12.1 server.
The XML format, with embedded images is used as a sample data delivered with the product. You may unzip NX_ROOT\samples\data\SampleData.zip and see the xml files in it.