FileFusion - Python Pdf Converter

Over the past few weeks, I’ve been developing FileFusion, a desktop application built with Python and Qt (PyQt5), designed to convert and merge files into PDFs in a clean, intuitive interface.

This project was both a technical deep dive and a UI/UX exercise, combining threaded background processing, file I/O handling, and dynamic Qt widgets to deliver a professional-grade user experience.

Overview🧩

FileFusion allows users to:

• 🗂️ Convert .doc, .docx, and common image formats (.png, .jpg, .bmp, .tiff) to PDF
• 📎 Merge multiple PDFs into a single document
• ⚙️ Track progress and conversion logs in real time
• 🖱️ Drag and drop files directly into the app
• 🧠 Handle both single and batch operations smoothly

The app’s UI adapts dynamically based on context, showing or hiding widgets such as the merge checkbox or output folder selector.

Architecture 🏗️

The app follows a modular MVC-like structure, with a clean separation between the engine (conversion logic) and the UI (PyQt5 front-end):

📂 Project Structure
├── converter_engine.py     # Core conversion and merging logic
├── app.py                 # Main window, threading, and UI logic
├── main_window_ui.py       # Generated PyQt5 UI file
├── preview_window.py       # PDF preview dialog
└── resources/
    ├── icons/
    └── styles.qss

Core Processing 🔧

At the heart of the system is the ConverterEngine class, a self-contained conversion and merge manager.
It supports:

• Document Conversion using docx2pdf
• Image Conversion with Pillow
• PDF Merging via PyPDF2.PdfMerger
• Progress Feedback through callback functions

Each conversion operation is saved to a temporary file, logged, and a cleanup system ensures this temporary files are properly deleted, even after errors.

 def _cleanup(self, file_paths: List[str]):
        """Removes temporary files."""
        for path in file_paths:
            try:
                os.remove(path)
                logging.info(f"Cleaned up temporary file: {path}")
            except OSError as e:
                logging.error(f"Error cleaning up file {path}: {e}")

Threading & Responsiveness 🧵

To keep the UI responsive, long-running conversions are handled on a background thread via a dedicated Worker object that communicates with the main thread using Qt signals:

class Worker(QObject):
    finished = pyqtSignal(bool, str, str)
    progress = pyqtSignal(int)
    status_update = pyqtSignal(str)

This allows real-time updates to the:

• Progress bar
• Status label
• Log messages

without blocking the main event loop.

User Interface & UX 🎨

The interface, built with Qt Designer

The style is designed around a dark, modern theme with a clear focus on usability:

• Drag-and-drop support for quick file input
• Dynamic widget visibility depending on user actions (e.g., merge mode hides output folder input)
• Consistent visual hierarchy using custom Qt stylesheet:

self.setStyleSheet("""
    QWidget { background-color: #2b2b2b; color: #ffffff; font-family: Segoe UI; }
    QPushButton { background-color: #0078d7; border-radius: 4px; }
    QPushButton:hover { background-color: #005a9e; }
    QProgressBar::chunk { background-color: #0078d7; border-radius: 4px; }
""")

The visual result is the following:

Design Decisions 🧠

A few important implementation choices:

• Threaded Processing
  Avoids freezing the UI and supports real-time progress reporting.
• Signal-based Communication
  Keeps background logic decoupled from UI updates, a must for Qt apps.
• Flexible Output Handling
  The convert_to_pdf() method now supports an optional output directory argument, ensuring clean separation between merge workflows and individual conversions.
• Automatic Resource Cleanup
  Temporary PDFs used for merging are safely deleted after completion to prevent file clutter.

Challenges & Lessons Learned 🧪

• Thread-safe logging required a custom Qt log handler that emits status updates to the GUI safely.
• PDF merging with PyPDF2 needed careful file handling (binary mode, file handles closed properly).
• Progress reporting had to work seamlessly across mixed file types and dynamic workloads.

Tech Stack 🧰

Takeaway 🏁

FileFusion was an excellent exercise in desktop application engineering with Python, balancing real-world file operations, asynchronous workflows, and user experience design.
It’s open for future extension, and demonstrates how Python, when combined with Qt, can produce clean, professional-grade applications beyond the command line.

Try it yourself !

If you want to try it, you can download it directly from here, unzip, and launch the .exe

Please note that this .exe might fire security warnings. This is a normal behaviour since this little app hasn’t been signed through a Certificate Authority (CA).