Combine JPG and PNG Images into PDF Online Combine multiple images into a single PDF document.

The tool works by using the pdf-lib library to create a new PDFDocument, into which it embeds images using either the embedJpg or embedPng methods, depending on the image type. When processing multiple files, it handles them sequentially, adding each one to the document as a separate page. To ensure proper scaling, it calculates the dimensions of each image and adjusts them to fit within the selected page size, whether that's A4, Letter, or a fit-to-image option, while maintaining the aspect ratio. The images are then centered on each page with 20pt margins. This process is facilitated by the use of React state management, specifically the useState hook, which stores the list of files to be processed, as well as other relevant data such as the current page size and any error messages that may occur during processing. The URL.createObjectURL method is used to generate a downloadable PDF file from the resulting Blob object, which contains the PDF bytes generated by pdf-lib's save method.

When users interact with the tool, their actions trigger various callbacks, including handleFile, removeFile, moveUp, and moveDown, each of which updates the state accordingly. The process callback is where the actual PDF generation occurs, using async/await to handle the promise returned by pdf-lib's create method. If an error occurs during processing, it is caught and stored in the error state, allowing for user notification. The useEffect hook ensures that any existing object URLs are revoked when the component unmounts or the result changes, preventing memory leaks. Throughout this process, React's useCallback hook helps optimize performance by memoizing frequently used functions and preventing unnecessary re-renders. By leveraging these technologies and techniques, the tool provides a seamless user experience while generating high-quality PDFs entirely in the browser.