Read lines from a file then search a different file using those values

grepfile.sh

#!/bin/bash
# Accepts in.txt as input
# Uses strings found in search.txt
# Outputs to out.txt

# Test if in.txt exists in pwd
if [ ! -f in.txt ]; then
  echo "Input data file not found. Please create in.txt"
  exit 1;
fi
# Test if search.txt exists in pwd
if [ ! -f search.txt ]; then
  echo "Search list file not found. Please create search.txt with 1 search string per line"
  exit 1;
fi

# Execute search
while read word; do
  grep "$word" in.txt;
done <search.txt >out.txt