getting ComException while reading the document in SharePoint 2010

Answer 1

Two things:

1. Make sure you dispose the stream (see this post)
2. Have you tried taking the file.length from the stream?

Alternatively just use the following code (from the top of my head)

byte[] content = file.OpenBinary();

Answer 2

Try checking out the file prior to opening. Also dispose of the stream as mentioned above.