PM> Install-Package Spire.Doc

using System.Drawing;
using Spire.Doc;
using Spire.Doc.Documents;
using System.Drawing.Imaging;

namespace HTMLToImage
{
    class Program
    {
        static void Main(string[] args)
        {
            //Create a Document instance
            Document mydoc = new Document();
           
            //Load an HTML sample document
            mydoc.LoadFromFile(@"sample.html", FileFormat.Html, XHTMLValidationType.None);
           
            //Save to image. You can convert HTML to BMP, JPEG, PNG, GIF, Tiff etc
            Image image = mydoc.SaveToImages(0, ImageType.Bitmap);
            image.Save("HTMLToImage.png", ImageFormat.Png);
        }
    }
}

Imports System.Drawing.Imaging
Imports Spire.Doc
Imports Spire.Doc.Documents

Namespace HTMLToImage
    Class Program
        Shared Sub Main(ByVal args() As String)
            'Create a Document instance
            Dim document As New Document()
            'Load an HTML sample document
            document.LoadFromFile("sample.html", FileFormat.Html, XHTMLValidationType.None)
            'Save to image. You can convert HTML to BMP, JPEG, PNG, GIF, Tiff etc
            Dim image As Image = document.SaveToImages(0, ImageType.Bitmap)
            image.Save("HTMLToImage.png", ImageFormat.Png)

        End Sub
    End Class
End Namespace

PM> Install-Package Spire.Doc

using Spire.Doc;
using Spire.Doc.Documents;
using System.Drawing;
using System.Drawing.Imaging;

namespace WordToTiff
{
    class Program
    {
        static void Main(string[] args)
        {
            // Create a Document object
            Document doc = new Document();

            // Load a Word document
            doc.LoadFromFile("C:\\Users\\Administrator\\Desktop\\input.docx");

            // Convert the whole document to images
            Image[] images = doc.SaveToImages(ImageType.Bitmap);

            // Convert multiple images into a TIFF file
            ConvertImagesToTiff(images, "ToTiff.tiff", EncoderValue.CompressionLZW);

            // Dispose resource
            doc.Dispose();
        }

        private static ImageCodecInfo GetEncoderInfo(string mimeType)
        {
            // Get the image encoders
            ImageCodecInfo[] encoders = ImageCodecInfo.GetImageEncoders();
            for (int j = 0; j < encoders.Length; j++)
            {
                // Find the encoder that matches the specified MIME type
                if (encoders[j].MimeType == mimeType)
                    return encoders[j];
            }
            throw new Exception(mimeType + " mime type not found in ImageCodecInfo");
        }

        public static void ConvertImagesToTiff(Image[] images, string outFile, EncoderValue compressEncoder)
        {
            // Set the encoder parameters 
            Encoder enc = Encoder.SaveFlag;
            EncoderParameters ep = new EncoderParameters(2);
            ep.Param[0] = new EncoderParameter(enc, (long)EncoderValue.MultiFrame);
            ep.Param[1] = new EncoderParameter(Encoder.Compression, (long)compressEncoder);

            // Get the first image
            Image pages = images[0];

            // Create a variable
            int frame = 0;

            // Get an ImageCodecInfo object for processing TIFF image codec information
            ImageCodecInfo info = GetEncoderInfo("image/tiff");

            // Iterate through each Image
            foreach (Image img in images)
            {
                // If it's the first frame, save it to the output file with specified encoder parameters
                if (frame == 0)
                {
                    pages = img;
                    pages.Save(outFile, info, ep);
                }
                else
                {
                    // Save the intermediate frames
                    ep.Param[0] = new EncoderParameter(enc, (long)EncoderValue.FrameDimensionPage);

                    pages.SaveAdd(img, ep);
                }

                // If it's the last frame, flush the encoder parameters and close the file
                if (frame == images.Length - 1)
                {
                    ep.Param[0] = new EncoderParameter(enc, (long)EncoderValue.Flush);
                    pages.SaveAdd(ep);
                }
                frame++;
            }
        }
    }
}

PM> Install-Package Spire.Doc

using Spire.Doc;

namespace ConvertRtfToHtml
{
    class Program
    {
        static void Main(string[] args)
        {
            //Create a Document instance
            Document document = new Document();

            //Load an RTF document 
            document.LoadFromFile("input.rtf");

            //Save as HTML format
            document.SaveToFile("RtfToHtml.html", FileFormat.Html);
        }
    }
}

using Spire.Doc;
using System.Drawing.Imaging;
using System.Drawing;
using Spire.Doc.Documents;

namespace ConvertRtfToImage

{
    class Program
    {
        static void Main(string[] args)
        {
            //Create a Document instance
            Document document = new Document();

            //Load an RTF document 
            document.LoadFromFile("input.rtf");

            //Convert the RTF document to images
            Image[] images = document.SaveToImages(ImageType.Bitmap);

            // Iterate through the image collection
            for (int i = 0; i < images.Length; i++)
            {
                //Save the image as png format
                string outputfile = string.Format("image-{0}.png", i);
                images[i].Save(outputfile, ImageFormat.Png);
            }
        }
    }
}

PM> Install-Package Spire.Doc

using Spire.Doc;

namespace ConvertToRtf
{
    class Program
    {
        static void Main(string[] args)
        {
            //Create a Word document instance
            Document document = new Document();

            //Load a Word sample document
            document.LoadFromFile("sample.docx");

            // Save the document to RTF
            document.SaveToFile("Result.rtf", FileFormat.Rtf);
        }

    }
}

Imports Spire.Doc

Namespace ConvertToRtf
    
    Class Program
        
        Private Shared Sub Main(ByVal args() As String)
            'Create a Word document instance
            Dim document As Document = New Document
            'Load a Word sample document
            document.LoadFromFile("sample.docx")
            'Save the document to RTF
            document.SaveToFile("Result.rtf", FileFormat.Rtf)
        End Sub
    End Class
End Namespace

using Spire.Doc;
using System;

public class RtfToDocDocx
{

    public static void Main(String[] args)
    {
        // Create a Document instance
        Document document = new Document();
        // Load an RTF document
        document.LoadFromFile("input.rtf", FileFormat.Rtf);
        // Save the document to Doc
        document.SaveToFile("toDoc.doc", FileFormat.Doc);
        // Save the document to Docx
        document.SaveToFile("toDocx.docx", FileFormat.Docx2013);
    }
}

Imports Spire.Doc
Imports System
Public Class RtfToDocDocx
    
    Public Shared Sub Main(ByVal args() As String)
        ' Create a Document instance
        Dim document As Document = New Document
        ' Load an RTF document
        document.LoadFromFile("input.rtf", FileFormat.Rtf)
        ' Save the document to Doc
        document.SaveToFile("toDoc.doc", FileFormat.Doc)
        ' Save the document to Docx
        document.SaveToFile("toDocx.docx", FileFormat.Docx2013)
    End Sub
End Class