i had a text file in soc part of the fpga which is linux running on it.now i am using a modem and copy it using a Ethernet cable to modem and another cable to pc using the commend
Technically this isn't even an FPGA question, it is a PC/Linux communication question and should have been posted in another section.
You probably need to use a Ethernet crossover cable (If you want a direct connection between the two), or connect them via a switch on the same network.
IIRC, crossover cables are much less commonly needed now that one end of the link either is 1000BaseT or supports auto-mdi-x. This can save time in the lab looking for specialty cables.
After connection has been confirmed and basic ping tests are done, you would need to know the remote ip and configure the PC adaptor to be on the same network. That should be enough. If not, it seems you can use scp -oBindAddress=<adaptor-ip> root@<remote_ip>:/home/root/out.txt /cygdrive/C/users