Someone

for i in CPU*; do num=$(echo "$i" | cut -c4 -); cp file$num.txt $i; done
[root@herlo-lap ~]# ls -lR CPU*
CPU1:
total 0
-rw-rw-r-- 1 root root 0 May 23 21:51 file1.txt

CPU3:
total 0
-rw-rw-r-- 1 root root 0 May 23 21:51 file3.txt

CPU4:
total 0
-rw-rw-r-- 1 root root 0 May 23 21:51 file4.txt

CPU5:
total 0
-rw-rw-r-- 1 root root 0 May 23 21:51 file5.txt

CPU6:
total 0
-rw-rw-r-- 1 root root 0 May 23 21:51 file6.txt