function pdf_extract
    if test (count $argv) -lt 4
        echo "Usage: pdf_extract <input_file> <from_page> <to_page> <output_file>"
        return 1
    end

    set input_file $argv[1]
    set from_page $argv[2]
    set to_page $argv[3]
    set output_file $argv[4]

    if not test -f $input_file
        echo "Error: input file '$input_file' not found"
        return 1
    end

    set tmp_prefix (string replace -r '\.pdf$' '' $input_file)_extract_tmp_

    pdfseparate -f $from_page -l $to_page $input_file "$tmp_prefix%04d.pdf" &&
    pdfunite $tmp_prefix*.pdf $output_file &&
    rm $tmp_prefix*.pdf
end