C++ :: Reading Stream Data From PDF Files Compressed In LZW?

I'm trying to read stream data from a stream in a pdf file compressed in LZW. My first step is to read this compressed data into a buffer. The second step is to decompress it. I know how to decompress it, it is the first step I am having trouble with.

How should I read this data? If I read each character into a char the numerical output will not exceed 256. LZW compressed output should exceed 256.

I read the pdf in binary mode and have tried the read function like below.

From what I understand (don't quote me), I should be reading in 12 bits at a time. Is that correct and if so should I be using a bitfield. If I do need a bitfield then how to I read the data from the stream into a bitfield of 12 bits without restricting the binary value of the characters being read from the compressed stream.

Code:
ifstream inputfilestream;
inputfilestream.open("myfile.pdf", ios::out | ios::binary);
char mychar; //unsigned char gives an error though it can be //converted to unsigned char later.
while (inputfilestream.read(mychar, 1)) {
// do something with the char.. I have stored it in an int vector
}