You cannot convert to PDF the actual shape file. You can either export to PDF the CAD document in which the shapefile is imported to, or you could simply open the *.shp using a text editor and print that source. But that's not actual conversion.
This conversion entry was verified by us and conversion was flagged as wrong or not possible.
Usually this happens when the conversion would try to convert different types of data between each other, such as audio to image, or it is not possible because incompatibility between programs, caused by closed file formats, very limited support etc.
If you find entry that you feel is flagged as bad wrongly, please tell us in the discussion below with as much as information as possible so we can fix it.