Extracting Names from Filename in Bash

Here you have a solution. I tested it an it creates the folders as you explained.

for filename in *.pdf
do
  echo "Processing file $filename "
  first_letter="${filename:0:1}"
  mkdir -p $first_letter #if already exists won't print error
  last_name=$(echo $filename | sed 's/\([^[:blank:]]\)\([[:upper:]]\)/\1 \2/g'  |awk '{print $1}')
  mkdir -p $first_letter/$last_name
  mv $filename $first_letter/$last_name
done

If the lastname is always the shortest trailing string staring with an upper case letter (there are no compound lastnames for example) you could use a shell parameter expansion of the form ${parameter%pattern} in place of a regex solution.

Ex.

for f in [[:upper:]]*[[:upper:]]*; do 
  d="${f:0:1}/${f%[[:upper:]]*}/"
  echo mkdir -p "$d"
  echo mv "$f" "$d"
done
mkdir -p D/Doe/
mv DoeJohn20190327 D/Doe/

Remove the echos when you are satisfied that it is doing the right thing.

See for example Parameter Expansion