Try this code:

#!/bin/bash
 # This loop is to count the number of bytes per line, then it will find the max number of bytes over all the lines
max=$(cat datafile| while IFS= read line; do echo "${line}" | wc -c; done | sort -k 1.1n | tail -n1)

cat datafile| while IFS= read line; do 
# Count of bytes in every line
n=$(echo "${line}" | wc -c)     

# bytes difference in every line
diff=$(echo $((${max}-${n})))  

# complete the number of bytes per line to the max number of bytes over all the lines.
dash=$(printf %"${diff}"s | tr " " ".")

# print results
echo ${line},${dash}
done

output:

Unix was ,....................
originally meant ,............
to be a ,.....................
co,...........................
nvenient p,...................
latform for progra,...........
mmers developing software to,.
be run on it and on other ,..
systems, rather than for non-,
programmers.,.................
[7][8] The system grew larger,
as the operating system star,
ted spreading in a,...........
cademic circ,.................
les, as users add,............
ed their own tools to th,.....
e system and shared them wi,..
th colleagues.,...............

Try this code:

#!/bin/bash
 # This loop is to count the number of bytes per line, then it will find the max number of bytes over all the lines
max=$(cat datafile| while IFS=" " read line; do echo "${line}" | wc -c; done | sort -k 1.1n | tail -n1)

cat datafile| while IFS=" " read line; do 
# Count of bytes in every line
n=$(echo "${line}" | wc -c)     

# bytes difference in every line
diff=$(echo $((${max}-${n})))  

# complete the number of bytes per line to the max number of bytes over all the lines.
dash=$(printf %"${diff}"s | tr " " ".")

# print results
echo ${line},${dash}
done

output:

Unix was,.....................
originally meant,.............
to be a,......................
co,...........................
nvenient p,...................
latform for progra,...........
mmers developing software to,.
be run on it and on other,....
systems, rather than for non-,
programmers.,.................
[7][8] The system grew larger,
as the operating system star,.
ted spreading in a,...........
cademic circ,.................
les, as users add,............
ed their own tools to th,.....
e system and shared them wi,..
th colleagues.,...............