This is my first bash script so I ask to you to say what you think.

The script must check every directory and it it find the pdf file on this directory: move file to parent directory, change the name of this file and remove directory.

So if I had this folder structure:

folder1
  file.pdf
  file.txt
folder2
  some.pdf
  another.pdf
folder3
  some.txt

the script must change it to:

 folder1.pdf
 folder2.pdf
 folder2_2.pdf
 folder3
   some.txt

Here is a script code:

#!/bin/bash

working_directory="$HOME/MEGAsync/downloads/books"

cd $working_directory

# for each directory in working directory
for D in `find . -type d`
do
    # skip '.'
    if [[ $D != "." ]]; then
        # get folder name 
        folder_name=${D##*/}
        # and cd to folder
        cd $D

        # number of pdf files in the current directory
        declare -i pdf_count=0
        # for each file in the current directory
        for f in *; do

            # get file without path
            file=$(basename "$f")
            extension="${file##*.}"
            filename="${file%.*}"

            if [[ $extension == 'pdf' ]]; then
                pdf_count=pdf_count+1
                if [[ pdf_count < 2 ]]; then
                    new_filename="${working_directory}/${folder_name}.pdf";
                else
                    new_filename="${working_directory}/${folder_name}_${pdf_count}.pdf";
                fi

                echo cp $working_directory/$folder_name/$f $new_filename
                cp $working_directory/$folder_name/$f $new_filename
            fi
        done
        
        # return to parent folder
        cd ..

        # delete directory if pdf-file was found
        if [[ $pdf_count != "0" ]]; then
            echo rm -R $working_directory/$folder_name
            rm -R $working_directory/$folder_name
        fi
    fi
done