This command
scp linuxnet.pdf [email protected]:linuxnet.pdf
Copies the local file linuxnet.pdf to the remote server 192.xxxx. It uses the user account zak and places the file in the remote user's home directory, named as linuxnet.pdf. Note that if 192.xxxx represents your Pi then it will have placed the file in Zak's home directory.
You said that you wanted to copy from the remote server to your local Windows client. In this case you should reverse the order of the arguments thus, and run the command from Cygwin:
scp [email protected]:linuxnet.pdf linuxnet.pdf
The lack of directory specification on the target filename means that it will be written to the current directory, whatever that is at the time you execute the copy.