dynamically display pdf to user

dynamically display pdf to user

Please i realy need help with this
I'm try to convert pdf to swf using this codes This is the working one
code explanation:
//docs: is the location the pdf is located.
echo exec("D:\wamp\www\dspzlibrary\converter\pdf2swf.exe docs/book.pdf -o
docs/book.swf -f -T 9 -t -s storeallcharacters");
why this one is not working
//file name $file = "vsomaths";
echo exec("D:\wamp\www\dspzlibrary\converter\pdf2swf.exe docs/$files.pdf
-o docs/$file.swf -f -T 9 -t -s storeallcharacters");
I want to execute the the exe function dynamically using selected file name.
Thanks alot.