Add and Edit Bookmarks in Your PDF Edit bookmarks.

The tool works under the hood by utilizing client-side JavaScript with React to handle user interactions and manage the PDF bookmark editing process. When a PDF file is loaded, it uses the `pdf-lib` library to parse the document and extract existing bookmarks from the outline tree. This involves traversing the hierarchical structure of bookmarks, extracting title, destination page, and level information for each bookmark, and storing this data in an array of Bookmark objects. The `useCallback` hook is used to memoize functions such as `handleFile`, `addBookmark`, `updateBookmark`, and `removeBookmark`, ensuring that these functions are not recreated unnecessarily and improving performance.

The tool also leverages the `useState` hook to manage state variables such as `file`, `bookmarks`, `editingId`, and `processing`, which are used to keep track of the current state of the application. When saving changes, it uses the `pdf-lib` library to build a new outline tree based on the updated bookmarks and then saves the modified PDF document using the `arrayBuffer` method. The resulting byte array is then processed and returned as a string, which can be downloaded or further manipulated by the user. Additionally, the tool uses responsive UI components such as `FileDropzone`, `InputWithHelp`, and `InfoHint` to provide an intuitive and user-friendly interface for editing PDF bookmarks.

In terms of browser APIs, the tool does not rely on any specific API for its core functionality, instead focusing on manipulating the PDF document using the `pdf-lib` library. However, it does use JavaScript features such as `crypto.randomUUID` to generate unique IDs for each bookmark and `arrayBuffer` to process the PDF file. The `PDFDocument`, `PDFName`, `PDFHexString`, and `PDFRef` classes from the `pdf-lib` library are used extensively throughout the code to represent and manipulate the PDF document structure. Overall, the tool's implementation is centered around React, JavaScript, and the `pdf-lib` library, providing a robust and efficient solution for editing PDF bookmarks.