Resize PDF Pages Online Resize PDF pages.

The tool utilizes client-side JavaScript with React to handle file processing and resizing locally within the browser, eliminating the need for external server uploads. It employs memoization through `useCallback` to optimize performance by preventing unnecessary re-renders of components. When a PDF file is dropped into the tool, it uses the `FileDropzone` component to accept the file and trigger the `handleFile` function, which updates the component's state with the selected file. The `process` function is then called, which imports the `PDFDocument` class from the `pdf-lib` library and loads the PDF file into a document object. This object allows for manipulation of the PDF's page sizes, which are set using the `setSize` method based on either the preset size or custom dimensions entered by the user.

The tool uses a dictionary called `PRESETS` to store predefined page sizes, such as A4 and Letter, with their corresponding width and height values in PDF points. When the user selects a preset size, the `preset` state variable is updated, and the corresponding width and height values are used to resize the PDF pages. If the user chooses to enter custom dimensions, the `customW` and `customH` state variables are updated, and these values are used to set the page sizes. The resized PDF is then saved as a blob using the `save` method of the `PDFDocument` object, and a URL object is created from this blob using the `URL.createObjectURL` method. This URL can be used to download the resized PDF file.

The tool's UI is built using responsive design principles, ensuring that it adapts to different screen sizes and devices. The `InputWithHelp` component is used to provide input fields for custom dimensions, along with hints and suffixes to guide the user in entering valid values. The `glass-button` class is applied to buttons to give them a consistent appearance throughout the UI. When an error occurs during processing, an error message is displayed using the `setError` state variable, and when the resizing process is complete, a success message is displayed along with a download button to allow the user to save the resized PDF file.