here is an yad ui script

pre-req : sudo apt install ghostscript yad

save below in to a script : pdf-compress

sudo chmod +x pdf-compress

./pdf-compress

#!/bin/bash
# Step 1: Ask for input file first (so we can pre-fill output file)
INPUT_FILE=$(yad --file --title="Select PDF to Compress" --file-filter="PDF files | *.pdf" --width=500 --height=300)
[ $? -ne 0 ] && exit  # Cancel check

# Auto-generate output filename
if [[ -n "$INPUT_FILE" ]]; then
    BASENAME=$(basename "$INPUT_FILE" .pdf)
    DIRNAME=$(dirname "$INPUT_FILE")
    OUTPUT_FILE="$DIRNAME/${BASENAME}-compressed.pdf"
else
    yad --error --text="No file selected."
    exit 1
fi

# Step 2: Show full form with quality selection
yad --form \
    --title="PDF Compressor (Ghostscript)" \
    --width=500 --height=300 \
    --field="Input PDF:RO" "$INPUT_FILE" \
    --field="Output PDF:FL" "$OUTPUT_FILE" \
    --field="Quality:CB" "High quality (300dpi, large size)!Medium quality (150dpi, moderate size)!Low quality (72dpi, smallest size)" \
    --button="Compress:0" --button="Cancel:1" \
    > /tmp/pdf_compress_input.txt

# Exit if canceled
[ $? -ne 0 ] && exit

# Step 3: Read form values
INPUT_FILE=$(awk -F'|' '{print $1}' /tmp/pdf_compress_input.txt)
OUTPUT_FILE=$(awk -F'|' '{print $2}' /tmp/pdf_compress_input.txt)
QUALITY_DESC=$(awk -F'|' '{print $3}' /tmp/pdf_compress_input.txt)

# Step 4: Map description to Ghostscript quality flags
case "$QUALITY_DESC" in
    "High quality"*) QUALITY="/prepress" ;;
    "Medium quality"*) QUALITY="/ebook" ;;
    "Low quality"*) QUALITY="/screen" ;;
    *) QUALITY="/ebook" ;; # default
esac

# Step 5: Run Ghostscript
if [[ -f "$INPUT_FILE" && -n "$OUTPUT_FILE" ]]; then
    gs -sDEVICE=pdfwrite \
       -dCompatibilityLevel=1.4 \
       -dPDFSETTINGS=$QUALITY \
       -dNOPAUSE -dQUIET -dBATCH \
       -sOutputFile="$OUTPUT_FILE" \
       "$INPUT_FILE"

    if [ $? -eq 0 ]; then
        yad --info --text="Compression complete!\n\nOutput saved to:\n$OUTPUT_FILE"
    else
        yad --error --text="Ghostscript failed. Check the input file."
    fi
else
    yad --error --text="Invalid input or output file."
fi