Crop and Trim PDF Pages Crop PDF pages.

The tool works by utilizing the pdf-lib library to load and manipulate PDF documents. When a file is dropped into the FileDropzone component, it triggers the handleFile function, which reads the file as an array buffer and loads it into a PDFDocument object using pdf-lib's load method with the ignoreEncryption option set to true. The getPageCount method of the PDFDocument object is then used to retrieve the total number of pages in the document, which is stored in the pageCount state variable.

The parsePages function takes a string input representing page ranges and returns an array of page indices. This function splits the input string into parts using commas as separators, trims each part, and filters out empty strings. It then iterates over each part, checking if it contains a hyphen to determine if it represents a range of pages or a single page number. If it's a range, the function extracts the start and end page numbers, checks if they are valid, and adds the corresponding page indices to a set. If it's a single page number, the function simply adds the page index to the set.

The process function is triggered when the user clicks the crop button, and it uses the pdf-lib library to manipulate the media and crop boxes of each page. It first checks if the file is valid and if at least one non-zero crop value has been entered. If these conditions are met, it retrieves the PDFDocument object, gets the total number of pages, and determines which pages to crop based on the page mode selected by the user. The function then iterates over each page index, retrieves the corresponding page object using the getPage method, and gets its media box dimensions using the getMediaBox method.

The tool uses the setMediaBox and setCropBox methods of the page object to apply the crop values entered by the user. It calculates the new width and height of the page by subtracting the left and right crop values from the original width and the top and bottom crop values from the original height. If the new dimensions are invalid, it displays an error message indicating that the crop values exceed the page dimensions.

The cropped PDF is then saved using the save method of the PDFDocument object, which returns a byte array representing the cropped document. This byte array is used to create a blob object, which is in turn used to create an object URL that can be used to download the cropped PDF. The URL.createObjectURL method is used to create this object URL, and the revokeObjectURL method is used to clean up any existing object URLs when the component unmounts.

The React library is used to manage the tool's state and handle user input. The useState hook is used to store the file, page count, crop values, and other state variables, while the useCallback hook is used to memoize functions like handleFile and process. The useEffect hook is used to clean up object URLs when the component unmounts.

The tool also uses various browser APIs, such as the arrayBuffer method of the File object to read the file contents, and the URL.createObjectURL method to create an object URL for downloading the cropped PDF. The Blob constructor is used to create a blob object from the byte array returned by the save method of the PDFDocument object.

The tool's client-side processing eliminates the need to upload sensitive documents to external servers, making it a reliable choice for tasks like cropping PDF pages online. The use of pdf-lib and React enables efficient and secure manipulation of PDF documents, while the attention to detail in handling crop values and page dimensions ensures that the resulting document is not corrupted or invalid.