i need a code that allows me to take an array search it on another txt file and replace the new string with the string after the (,) and save the changes in a new file. how do i do that????

i have this:
file1.txt
sd00100 test on 24 ago
sd00145 test on 12 jun
sd00120 test on 14 ene

and this:
file2.txt
sd00100, sf1254
sd00145,sf2446
sd00120,sg5465

and i need to have this result:
file1_new.txt
sf1254 test on 24 ago
sf2446 test on 12 jun
sg5465 test on 14 ene
:-|