feat: add --decrypt mode for password-protected PDFs

README.md

@@ -35,7 +35,7 @@ passifypdf --help
 ```
 
 
-Sample Run:
+Sample Run (Encrypt):
 ```bash
 passifypdf -i input.pdf -o protected.pdf -p mySecretPassword
 
@@ -44,6 +44,15 @@ passifypdf -i input.pdf -o protected.pdf -p mySecretPassword
 # PDF file encrypted successfully and saved as 'protected.pdf'
 ```
 
+Sample Run (Decrypt):
+```bash
+passifypdf -i protected.pdf -o unlocked.pdf -p mySecretPassword --decrypt
+
+# -------------------------Sample output----------------------
+# Congratulations!
+# PDF file decrypted successfully and saved as 'unlocked.pdf'
+```
+
 ## Known Issues
 If you have nay special chars(example: an emoji like Star 🌟) in the PDF file, it gives a minor complain during execution. 
 But it still does the job, so you can ingore that "char or object error" which you see in the output.
@@ -53,4 +62,4 @@ In general you can use passifypdf to protect your PDF files against chance attac
 But you should not rely on this for mission-critical data or situation.
 
 ## Build & Run Locally
-Visit [BUILD.md](BUILD.md)
+Visit [BUILD.md](BUILD.md)

docs/CLI_OPTIONS.md

@@ -5,14 +5,18 @@ The `passifypdf` tool accepts the following command-line arguments:
 | Option | Long Option | Required | Description |
 | :--- | :--- | :--- | :--- |
 | `-i` | `--input` | Yes | Path to the input PDF file. |
-| `-o` | `--output` | Yes | Path to the output (encrypted) PDF file. |
-| `-p` | `--passwd` | Yes | Password to use for encryption. **Avoid passing sensitive passwords directly on the command line, as they may be exposed via process listings and shell history.** |
+| `-o` | `--output` | Yes | Path to the output (encrypted/decrypted) PDF file. |
+| `-p` | `--passwd` | Yes | Password to use for encryption/decryption. **Avoid passing sensitive passwords directly on the command line, as they may be exposed via process listings and shell history.** |
+|  | `--decrypt` | No | Decrypt an encrypted PDF instead of encrypting a plain PDF. |
 | `-v` | `--version` | No | Show the program's version number and exit. |
 | `-h` | `--help` | No | Show the help message and exit. |
 
 ## Example Usage
 
 ```bash
-# Using the installed CLI command (after `poetry install`)
+# Encrypt a PDF
 passifypdf -i input.pdf -o protected.pdf -p mySecretPassword
+
+# Decrypt a password-protected PDF
+passifypdf -i protected.pdf -o unlocked.pdf -p mySecretPassword --decrypt
 ```

passifypdf/cli.py

@@ -1,13 +1,32 @@
-import argparse
-
-
-def get_arg_parser() -> argparse.ArgumentParser:
-    arg_parser = argparse.ArgumentParser(
-        description="Encrypt a PDF file with a password of your choice.",
-        epilog="For more information, visit: https://github.com/SUPAIDEAS/passifypdf"
-    )
-    arg_parser.add_argument("-v", "--version", action="version", version="%(prog)s 1.0")
-    arg_parser.add_argument("-i", "--input", required=True, help="Path to the input PDF file to be encrypted")
-    arg_parser.add_argument("-o", "--output", required=True, help="Path where the encrypted PDF file will be saved")
-    arg_parser.add_argument("-p", "--passwd", required=True, type=str, help="Password to encrypt the PDF file with")
-    return arg_parser
+import argparse
+
+
+def get_arg_parser() -> argparse.ArgumentParser:
+    arg_parser = argparse.ArgumentParser(
+        description=(
+            "Encrypt a PDF file with a password, or decrypt an encrypted PDF "
+            "using --decrypt."
+        ),
+        epilog="For more information, visit: https://github.com/SUPAIDEAS/passifypdf",
+    )
+    arg_parser.add_argument("-v", "--version", action="version", version="%(prog)s 1.0")
+    arg_parser.add_argument("-i", "--input", required=True, help="Path to the input PDF file")
+    arg_parser.add_argument(
+        "-o",
+        "--output",
+        required=True,
+        help="Path where the processed PDF file (encrypted/decrypted) will be saved",
+    )
+    arg_parser.add_argument(
+        "-p",
+        "--passwd",
+        required=True,
+        type=str,
+        help="Password to encrypt/decrypt the PDF file",
+    )
+    arg_parser.add_argument(
+        "--decrypt",
+        action="store_true",
+        help="Decrypt an encrypted PDF instead of encrypting a plain PDF",
+    )
+    return arg_parser

passifypdf/encryptpdf.py

@@ -1,14 +1,37 @@
-"""Core PDF encryption module."""
+"""Core PDF encryption and decryption module."""
 
 import sys
 from pathlib import Path
-from typing import Union
+from typing import Tuple, Union
 
 from pypdf import PdfReader, PdfWriter
+from pypdf.errors import PdfReadError
 
 from .cli import get_arg_parser
 
 
+def _load_pdf_reader(input_pdf: Union[str, Path]) -> Tuple[Path, PdfReader]:
+    """Validate that input is an existing PDF file and return its reader."""
+    input_path = Path(input_pdf)
+    if not input_path.exists():
+        raise FileNotFoundError(f"Input file '{input_pdf}' not found.")
+
+    if not input_path.is_file():
+        raise IsADirectoryError(f"Input path '{input_pdf}' is not a file.")
+
+    invalid_pdf_error = ValueError(f"Input file '{input_pdf}' is not a valid PDF file.")
+    with input_path.open("rb") as source_file:
+        if source_file.read(5) != b"%PDF-":
+            raise invalid_pdf_error
+
+    try:
+        reader = PdfReader(input_path)
+    except PdfReadError as exc:
+        raise invalid_pdf_error from exc
+
+    return input_path, reader
+
+
 def encrypt_pdf(input_pdf: Union[str, Path], output_pdf: Union[str, Path], password: str) -> None:
     """
     Encrypts a PDF file with a password.
@@ -21,32 +44,48 @@ def encrypt_pdf(input_pdf: Union[str, Path], output_pdf: Union[str, Path], passw
     Raises:
         FileNotFoundError: If the input PDF file does not exist.
         IsADirectoryError: If the input path is a directory.
-        Exception: For other errors during processing.
+        ValueError: If the input file is not a valid PDF.
     """
-    input_path = Path(input_pdf)
-    if not input_path.exists():
-        raise FileNotFoundError(f"Input file '{input_pdf}' not found.")
+    _, reader = _load_pdf_reader(input_pdf)
+    writer = PdfWriter()
 
-    if not input_path.is_file():
-        raise IsADirectoryError(f"Input path '{input_pdf}' is not a file.")
+    for page in reader.pages:
+        writer.add_page(page)
 
-    try:
-        reader = PdfReader(input_path)
-        writer = PdfWriter()
+    writer.encrypt(password)
 
-        # Add all pages from the reader to the writer
-        for page in reader.pages:
-            writer.add_page(page)
+    with open(output_pdf, "wb") as f:
+        writer.write(f)
 
-        # Encrypt with a password
-        writer.encrypt(password)
 
-        # Write the encrypted PDF to a new PDF file passed as param
-        with open(output_pdf, "wb") as f:
-            writer.write(f)
+def decrypt_pdf(input_pdf: Union[str, Path], output_pdf: Union[str, Path], password: str) -> None:
+    """
+    Decrypts a password-protected PDF file.
 
-    except Exception as e:
-        raise Exception(f"Failed to encrypt PDF: {e}")
+    Args:
+        input_pdf (Union[str, Path]): Path to the encrypted input PDF file.
+        output_pdf (Union[str, Path]): Path to the decrypted output PDF file.
+        password (str): Password to decrypt the PDF with.
+
+    Raises:
+        FileNotFoundError: If the input PDF file does not exist.
+        IsADirectoryError: If the input path is a directory.
+        ValueError: If input is not a valid PDF, is not encrypted, or password is incorrect.
+    """
+    _, reader = _load_pdf_reader(input_pdf)
+
+    if not reader.is_encrypted:
+        raise ValueError(f"Input file '{input_pdf}' is not encrypted.")
+
+    if reader.decrypt(password) == 0:
+        raise ValueError(f"Failed to decrypt '{input_pdf}'. Please provide the correct password.")
+
+    writer = PdfWriter()
+    for page in reader.pages:
+        writer.add_page(page)
+
+    with open(output_pdf, "wb") as f:
+        writer.write(f)
 
 
 def main() -> int:
@@ -60,13 +99,17 @@ def main() -> int:
     args = arg_parser.parse_args()
 
     try:
-        encrypt_pdf(args.input, args.output, args.passwd)
-        print(f"Congratulations!\nPDF file encrypted successfully and saved as '{args.output}'")
+        if args.decrypt:
+            decrypt_pdf(args.input, args.output, args.passwd)
+            print(f"Congratulations!\nPDF file decrypted successfully and saved as '{args.output}'")
+        else:
+            encrypt_pdf(args.input, args.output, args.passwd)
+            print(f"Congratulations!\nPDF file encrypted successfully and saved as '{args.output}'")
         return 0
     except Exception as e:
         print(f"Error: {e}", file=sys.stderr)
         return 1
 
 
 if __name__ == "__main__":
-    sys.exit(main())
+    sys.exit(main())