I am unable to read some PDF documents on my Kindle 4, they are not too complex (I usually read more complex ones as paper with a lot of colora and images). Someone could you tell me the reason?
After some test I observed that Kindle 4 sometimes hangs reading PDF using a version greater than 1.4.
I suggest to use Ghostscript to convert the PDF document to the 1.4 version. The command is:
gs -dNOPAUSE -dBATCH -dFILTERVECTOR -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook -sProcessColorModel=DeviceGray -sColorConversionStrategy=Gray -dOverrideICC -dCompressFonts=true -r150 -sOutputFile=/home/path/to/output.pdf /home/path/to/input.pdf