Unix and Linux GNU coreutils command paste can be useful to merge corresponding or subsequent lines of files. Here is simple example of it’s usage:
viper@viper-laptop:~$ cat /tmp/test
pop
pop1
pop2
viper@viper-laptop:~$ cat /tmp/test1
1
2
3
4
viper@viper-laptop:~$ paste /tmp/test /tmp/test1
pop 1
pop1 2
pop2 3
4