a few shell (bash) solutions:

cd some_dir

for f in Test*.txt ; do cat /tmp/commonfile.txt $f > Final.$f ; done
find Test*.txt -maxdepth 0 -exec cat /tmp/commonfile.txt {} > Final.{}
+ \;
for n in `seq 1 100`; do cat /tmp/commonfile.txt Test$n.txt > Final$n.
+txt ; done
[download]

The middle one will be more portable .. note that the third one produces different final naming scheme.