Splitting Big PDF Documents into Smaller Files Efficiently

Updated on Jun 9, 2026

Environment

Version	Product	Author
2025.1.205	RadPdfProcessing	Desislava Yordanova

Description

When working with large PDF documents, you may need to split them into smaller "chunks" of a specified number of pages. This article shows how to export subsets of pages efficiently without repeatedly re-importing the entire document for each chunk.

Solution

To efficiently export subsets of pages from a large PDF document, use the PdfStreamWriter feature of RadPdfProcessing. This approach improves performance and reduces memory usage, making it ideal for processing large volumes of PDFs. The following steps show how to split a PDF document into smaller "chunks" using PdfStreamWriter.

Step 1: Include the Necessary Namespaces

Include the following namespaces in your project:

csharp

using Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Streaming;
using Telerik.Windows.Documents.Fixed.Model;

Step 2: Implement the Splitting Logic

Use the following logic to split a PDF document into smaller chunks. This example splits a document into chunks of 10 pages each, but you can adjust the pagesCount variable to change the chunk size as needed.

csharp

internal class Program
{
    public const string ResultDirName = @"..\..\..\Demo results";
    public const string InputFileMultipageDocument = "YourLargePDF.pdf";
    static void Main(string[] args)
    {
        EnsureEmptyResultDirectory();
        SplitDocumentPages("YourLargePDF_Chunk[{0}-{1}].pdf");
    }

    private static void SplitDocumentPages(string resultFileFormat)
    {
        string documentToSplit = InputFileMultipageDocument;
        int pagesCount = 10; // Number of pages per chunk
        using (PdfFileSource fileToSplit = new PdfFileSource(File.OpenRead(documentToSplit)))
        {
            int totalPages = fileToSplit.Pages.Length;
            int currentTotalPageIndex = 0;
            int numberOfSplitDocs = totalPages / pagesCount + (totalPages % pagesCount == 0 ? 0 : 1);

            for (int docIndex = 0; docIndex < numberOfSplitDocs; docIndex++)
            {
                int currentPagesEnd = Math.Min(currentTotalPageIndex + pagesCount, totalPages);
                string splitDocumentName = Path.Combine(ResultDirName, string.Format(resultFileFormat, docIndex * pagesCount + 1, currentPagesEnd));

                using (PdfStreamWriter fileWriter = new PdfStreamWriter(File.OpenWrite(splitDocumentName)))
                {
                    for (int pageIndex = currentTotalPageIndex; pageIndex < currentPagesEnd; pageIndex++)
                    {
                        PdfPageSource page = fileToSplit.Pages[pageIndex];
                        fileWriter.WritePage(page);
                        currentTotalPageIndex++;
                    }
                }
            }
        }
    }

    private static void EnsureEmptyResultDirectory()
    {
        if (Directory.Exists(ResultDirName))
        {
            foreach (string fileName in Directory.EnumerateFiles(ResultDirName))
            {
                File.Delete(fileName);
            }
        }
        else
        {
            Directory.CreateDirectory(ResultDirName);
        }
    }
}

This solution processes the splitting operation by writing each chunk directly to a new file without the need to re-import the original document multiple times:

See Also

• PdfStreamWriter
• RadPdfProcessing