For video conversion, HandBrake remains the industry standard. It's completely free and open-source, allowing you to convert nearly any video format into MP4 or MKV with professional-grade control over codecs and quality.
While primarily an office suite, it’s one of the best free tools for document conversion. It can open almost any Microsoft Office format and export it to PDF or other open formats with high fidelity. Commonly Supported Formats file converter free download
If you need to handle images, XnConvert supports over 500 formats. It allows you to create "actions" like resizing, watermarking, and converting thousands of photos in one go. For video conversion