Combine Multiple PDFs Into One File Merge multiple PDFs.

The PDF Merge tool relies on client-side JavaScript, utilizing the React library to manage its state and user interactions. It employs memoization through useCallback to optimize performance by preventing unnecessary re-renders of components when their dependencies change. The core merging functionality is handled by the pdf-lib library, which allows it to create, read, and modify PDF documents. When a user adds PDF files, they are stored in an array of File objects, with each file's name and size displayed in the UI. The tool uses the Array.prototype.filter method to remove files from this array when the user chooses to delete them.

When the merge process is initiated, it checks if at least two PDF files have been added, displaying an error message if not. It then sets a processing flag to prevent concurrent merges and clears any previous errors. The pdf-lib library is used to create a new PDFDocument, into which pages from each of the selected PDFs are copied using the copyPages method. These pages are then added to the new document in the order they were selected, allowing for reordering via the moveFile function, which swaps the positions of two files in the array by creating a new array with the elements rearranged.

The merged PDF is saved as an array buffer, converted to a Blob object with the application/pdf MIME type, and then to a URL using URL.createObjectURL. This URL is used to create a downloadable link for the merged PDF. The tool also uses browser APIs such as URL.revokeObjectURL to clean up after itself when the component unmounts or the user resets the merge process, preventing memory leaks. Throughout this process, the tool maintains responsiveness by updating its UI dynamically based on the current state of the merge operation.

In terms of data structures, the tool primarily uses arrays to store and manipulate the list of PDF files, as well as objects to represent individual files and their properties. The use of React's useState hook allows it to manage this state effectively and trigger re-renders when necessary. By combining these technologies - client-side JavaScript, React, pdf-lib, and browser APIs - the tool provides a seamless and efficient way to merge PDFs directly in the browser, without requiring server uploads or additional software installations.