How to Compress PDF Document in C#, VB.NET

using Spire.Pdf;

namespace CompressPDF
{
    class Program
    {
        static void Main(string[] args)
        {
            //Loads the PDF document
            PdfDocument doc = new PdfDocument("Test.pdf");
            //Disables the incremental update
            doc.FileInfo.IncrementalUpdate = false;
            //Sets the compression level to best
            doc.CompressionLevel = PdfCompressionLevel.Best;
            //Saves and closes the resultant document
            doc.SaveToFile("Compressed.pdf");
            doc.Close();
        }
    }
}

Imports Spire.Pdf

Namespace CompressPDF
	Class Program
		Private Shared Sub Main(args As String())
			'Loads the PDF document
Dim doc As New PdfDocument("Test.pdf")
'Disables the incremental update
doc.FileInfo.IncrementalUpdate = False
'Sets the compression level to best
doc.CompressionLevel = PdfCompressionLevel.Best
'Saves and closes the resultant document
doc.SaveToFile("Compressed.pdf")
doc.Close()		
End Sub
	End Class
End Namespace

using Spire.Pdf;
using Spire.Pdf.Graphics;
using System.Drawing;

namespace CompressPDFImage
{
    class Program
    {
        static void Main(string[] args)
        {
            //Loads the PDF document
            PdfDocument doc = new PdfDocument("Image.pdf");
            //Disables the incremental update
            doc.FileInfo.IncrementalUpdate = false;

            //Traverses all pages
            foreach (PdfPageBase page in doc.Pages)
            {
                //Extracts images from page
                Image[] images = page.ExtractImages();
                if (images != null && images.Length > 0)
                {
                    //Traverses all images
                    for (int j = 0; j < images.Length; j++)
                    {
                        Image image = images[j];
                        PdfBitmap bp = new PdfBitmap(image);
                        //Reduces the quality of the image
                        bp.Quality = 20;
                        //Replaces the old image in the document with the compressed image
                        page.ReplaceImage(j, bp);
                    }
                }
            }
            //Saves and closes the resultant document
            doc.SaveToFile("Output.pdf");
            doc.Close();
        }
    }
}

Imports Spire.Pdf
Imports Spire.Pdf.Graphics
Imports System.Drawing

Namespace CompressPDFImage
	Class Program
		Private Shared Sub Main(args As String())
			'Loads the PDF document
Dim doc As New PdfDocument("Image.pdf")
'Disables the incremental update
doc.FileInfo.IncrementalUpdate = False

'Traverses all pages
For Each page As PdfPageBase In doc.Pages
	'Extracts images from page
	Dim images As Image() = page.ExtractImages()
	If images IsNot Nothing AndAlso images.Length > 0 Then
		'Traverses all images
		For j As Integer = 0 To images.Length - 1
			Dim image As Image = images(j)
			Dim bp As New PdfBitmap(image)
			'Reduces the quality of the image
			bp.Quality = 20
			'Replaces the old image in the document with the compressed image
			page.ReplaceImage(j, bp)
		Next
	End If
Next
'Saves and closes the resultant document
doc.SaveToFile("Output.pdf")
doc.Close()
		End Sub
	End Class
End Namespace