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By default, GroupDocs.Viewer saves output results to the local disk. Also, it can provide results as a stream.

To provide output results as a stream, use one of the following interfaces:

IFileStreamFactory defines methods to instantiate and release the output file streams.
IPageStreamFactory defines methods to instantiate and release the output page streams.
IResourceStreamFactory defines the methods to create resource URLs, instantiate, and release output HTML resource streams.

Use these interface as follows:

When rendering to PDF, implement the IFileStreamFactory interface and pass the implementation to the PdfViewOptions constructor.
When rendering to JPG/PNG or HTML with embedded resources, implement the IPageStreamFactory interface and pass the implementation to the JpgViewOptions/PngViewOptions constructor or to the HtmlViewOptions ForEmbeddedResources factory method.
When rendering into HTML with external resources, implement the IPageStreamFactory and IResourceStreamFactory interfaces and pass the implementation to the JpgViewOptions/PngViewOptions constructor or to the HtmlViewOptions ForExternalResources factory method.

The following code snippet shows how to render to HTML with embedded resources and to provide the output result as a stream. To do this, it implements the IPageStreamFactory interface only.

using System.IO;
using System.Collections.Generic;
using GroupDocs.Viewer;
using GroupDocs.Viewer.Options;
using GroupDocs.Viewer.Interfaces;
// ...

// Create the list to store output pages
List<MemoryStream> pages = new List<MemoryStream>();

using (Viewer viewer = new Viewer("sample.docx"))
{
    MemoryPageStreamFactory pageStreamFactory = new MemoryPageStreamFactory(pages);
    ViewOptions viewOptions = HtmlViewOptions.ForEmbeddedResources(pageStreamFactory);
    viewer.View(viewOptions);
}

internal class MemoryPageStreamFactory : IPageStreamFactory
{
    private readonly List<MemoryStream> _pages;

    public MemoryPageStreamFactory(List<MemoryStream> pages)
    {
        _pages = pages;
    }

    public Stream CreatePageStream(int pageNumber)
    {
        MemoryStream pageStream = new MemoryStream();
        _pages.Add(pageStream);
        return pageStream;
    }

    public void ReleasePageStream(int pageNumber, Stream pageStream)
    {
        //Do not release page stream as we'll need to keep the stream open
    }
}

VB.NET

Imports System.IO
Imports GroupDocs.Viewer
Imports GroupDocs.Viewer.Options
Imports GroupDocs.Viewer.Interfaces
' ...

Module Program
    Sub Main(args As String())
        ' Create the list to store output pages
        Dim pages As New List(Of MemoryStream)()

        Using viewer As New Viewer("sample.docx")
            Dim pageStreamFactory As New MemoryPageStreamFactory(pages)
            Dim viewOptions As ViewOptions = HtmlViewOptions.ForEmbeddedResources(pageStreamFactory)
            viewer.View(viewOptions)
        End Using
    End Sub

    Class MemoryPageStreamFactory
        Implements IPageStreamFactory

        Private ReadOnly _pages As List(Of MemoryStream)

        Public Sub New(pages As List(Of MemoryStream))
            _pages = pages
        End Sub

        Public Function CreatePageStream(pageNumber As Integer) As Stream Implements IPageStreamFactory.CreatePageStream
            Dim pageStream As New MemoryStream()
            _pages.Add(pageStream)
            Return pageStream
        End Function

        Public Sub ReleasePageStream(pageNumber As Integer, pageStream As Stream) _
            Implements IPageStreamFactory.ReleasePageStream
            'Do not release page stream as we'll need to keep the stream open
        End Sub
    End Class
End Module

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