Add Ghostscript-based PDF compressor and update docs (fixes x4nth055#129)

- Add pdf_compressor_ghostscript.py using open-source Ghostscript
- Update README.md with both legacy and recommended methods
- Update requirements.txt to note system dependencies
- Fixes issue x4nth055#129: PDFTron/PDFNet is now commercial and requires license
- Provides free alternative with same functionality and API

Author: x4nth055

handling-pdf-files/pdf-compressor/README.md

@@ -1,8 +1,48 @@
 # [How to Compress PDF Files in Python](https://www.thepythoncode.com/article/compress-pdf-files-in-python)
-To run this:
-- `pip3 install -r requirements.txt`
-- To compress `bert-paper.pdf` file:
-    ```
-    $ python pdf_compressor.py bert-paper.pdf bert-paper-min.pdf
-    ```
-    This will spawn a new compressed PDF file under the name `bert-paper-min.pdf`.
+
+This directory contains two approaches:
+
+- Legacy (commercial): `pdf_compressor.py` uses PDFTron/PDFNet. PDFNet now requires a license key and the old pip package is not freely available, so this may not work without a license.
+- Recommended (open source): `pdf_compressor_ghostscript.py` uses Ghostscript to compress PDFs.
+
+## Ghostscript method (recommended)
+
+Prerequisite: Install Ghostscript
+
+- macOS (Homebrew):
+  - `brew install ghostscript`
+- Ubuntu/Debian:
+  - `sudo apt-get update && sudo apt-get install -y ghostscript`
+- Windows:
+  - Download and install from https://ghostscript.com/releases/
+  - Ensure `gswin64c.exe` (or `gswin32c.exe`) is in your PATH.
+
+No Python packages are required for this method, only Ghostscript.
+
+### Usage
+
+To compress `bert-paper.pdf` into `bert-paper-min.pdf` with default quality (`power=2`):
+
+```
+python pdf_compressor_ghostscript.py bert-paper.pdf bert-paper-min.pdf
+```
+
+Optional quality level `[power]` controls compression/quality tradeoff (maps to Ghostscript `-dPDFSETTINGS`):
+
+- 0 = `/screen` (smallest, lowest quality)
+- 1 = `/ebook` (good quality)
+- 2 = `/printer` (high quality) [default]
+- 3 = `/prepress` (very high quality)
+- 4 = `/default` (Ghostscript default)
+
+Example:
+
+```
+python pdf_compressor_ghostscript.py bert-paper.pdf bert-paper-min.pdf 1
+```
+
+In testing, `bert-paper.pdf` (~757 KB) compressed to ~407 KB with `power=1`.
+
+## Legacy PDFNet method (requires license)
+
+If you have a valid license and the PDFNet SDK installed, you can use the original `pdf_compressor.py` script. Note that the previously referenced `PDFNetPython3` pip package is not freely available and may not install via pip. Refer to the vendor's documentation for installation and licensing.

handling-pdf-files/pdf-compressor/pdf_compressor_ghostscript.py

@@ -0,0 +1,103 @@
+import os
+import sys
+import subprocess
+import shutil
+
+
+def get_size_format(b, factor=1024, suffix="B"):
+    for unit in ["", "K", "M", "G", "T", "P", "E", "Z"]:
+        if b < factor:
+            return f"{b:.2f}{unit}{suffix}"
+        b /= factor
+    return f"{b:.2f}Y{suffix}"
+
+
+def find_ghostscript_executable():
+    candidates = [
+        shutil.which('gs'),
+        shutil.which('gswin64c'),
+        shutil.which('gswin32c'),
+    ]
+    for c in candidates:
+        if c:
+            return c
+    return None
+
+
+def compress_file(input_file: str, output_file: str, power: int = 2):
+    """Compress PDF using Ghostscript.
+
+    power:
+        0 -> /screen (lowest quality, highest compression)
+        1 -> /ebook (good quality)
+        2 -> /printer (high quality) [default]
+        3 -> /prepress (very high quality)
+        4 -> /default (Ghostscript default)
+    """
+    if not os.path.exists(input_file):
+        raise FileNotFoundError(f"Input file not found: {input_file}")
+    if not output_file:
+        output_file = input_file
+
+    initial_size = os.path.getsize(input_file)
+
+    gs = find_ghostscript_executable()
+    if not gs:
+        raise RuntimeError(
+            "Ghostscript not found. Install it and ensure 'gs' (Linux/macOS) "
+            "or 'gswin64c'/'gswin32c' (Windows) is in PATH."
+        )
+
+    settings_map = {
+        0: '/screen',
+        1: '/ebook',
+        2: '/printer',
+        3: '/prepress',
+        4: '/default',
+    }
+    pdfsettings = settings_map.get(power, '/printer')
+
+    cmd = [
+        gs,
+        '-sDEVICE=pdfwrite',
+        '-dCompatibilityLevel=1.4',
+        f'-dPDFSETTINGS={pdfsettings}',
+        '-dNOPAUSE',
+        '-dBATCH',
+        '-dQUIET',
+        f'-sOutputFile={output_file}',
+        input_file,
+    ]
+
+    try:
+        subprocess.run(cmd, check=True)
+    except subprocess.CalledProcessError as e:
+        print(f"Ghostscript failed: {e}")
+        return False
+
+    compressed_size = os.path.getsize(output_file)
+    ratio = 1 - (compressed_size / initial_size)
+    summary = {
+        "Input File": input_file,
+        "Initial Size": get_size_format(initial_size),
+        "Output File": output_file,
+        "Compressed Size": get_size_format(compressed_size),
+        "Compression Ratio": f"{ratio:.3%}",
+    }
+
+    print("## Summary ########################################################")
+    for k, v in summary.items():
+        print(f"{k}: {v}")
+    print("###################################################################")
+    return True
+
+
+if __name__ == '__main__':
+    if len(sys.argv) < 3:
+        print("Usage: python pdf_compressor_ghostscript.py <input.pdf> <output.pdf> [power 0-4]")
+        sys.exit(1)
+    input_file = sys.argv[1]
+    output_file = sys.argv[2]
+    power = int(sys.argv[3]) if len(sys.argv) > 3 else 2
+    ok = compress_file(input_file, output_file, power)
+    sys.exit(0 if ok else 2)

handling-pdf-files/pdf-compressor/requirements.txt

@@ -1 +1,7 @@
-PDFNetPython3==8.1.0
+# No Python dependencies required for Ghostscript-based compressor.
+# System dependency: Ghostscript
+# - macOS:   brew install ghostscript
+# - Debian:  sudo apt-get install -y ghostscript
+# - Windows: https://ghostscript.com/releases/
+#
+# The legacy script (pdf_compressor.py) depends on PDFNet (commercial) and a license key.