How to Create a PNG Thumbnail of the First Page of a Document

This guide explains how to create a PNG thumbnail for the first page of a document.

PrizmDoc Server does not currently allow you to extract specific pages and resize to PNG in a single operation. However, you can still accomplish this efficiently as a simple, two-step process:

1. Extract just the first page to a temporary PDF (which you never need to actually download)
2. Convert that temporary PDF to a thumbnail PNG

Here's how you do that in code.

First, create a PrizmDocServerClient:

var prizmDocServer = new PrizmDocServerClient(/* your connection info */);

Then, extract just the first page to a temporary PDF by calling ConvertToPdfAsync, passing in a ConversionSourceDocument with a pages argument set to "1":

var tempFirstPagePdf = await prizmDocServer.ConvertToPdfAsync(new ConversionSourceDocument("project-proposal.docx", pages: "1"));

This will upload the file to PrizmDoc Server, ask PrizmDoc Server to convert pages 2 and following to a PDF, and then return once the conversion is complete.

The returned result is just metadata about the output; the actual temporary PDF file has not been downloaded. And, in this case, we don't even need to download it. Instead, we'll just use it as input to another operation.

Next, we convert this temporary PDF to a thumbnail PNG by calling ConvertAsync:

var thumbnailPngs = await prizmDocServer.ConvertAsync(new ConversionSourceDocument(tempFirstPagePdf.RemoteWorkFile), new DestinationOptions(DestinationFileFormat.Png)
{
    PngOptions = new PngDestinationOptions() {
        MaxWidth = "512px",
        MaxHeight = "512px"
    }
});

This will start a conversion of the temporary PDF to a PNG which will not be larger than the specified maxWidth and maxHeight and then return when the conversion is finished. When converting to PNG, ConvertAsync always returns a collection of results, one result for each page that was converted to a PNG. In our case, there is just one page.

Finally, to actually download the single PNG result, call SaveAsync on the single result:

await thumbnailPngs.Single().RemoteWorkFile.SaveAsync("thumbnail.png");

Notice an important and powerful concept here: It is possible to pass the output of one operation as input to a second operation without downloading and re-uploading the temporary file from and to PrizmDoc Server. You can construct a ConversionSourceDocument using either a local file path or an existing RemoteWorkFile. The SDK will automatically upload the files for any ConversionSourceDocument instances which use a local file path and automatically reuse the existing RemoteWorkFile for any ConversionSourceDocument instances constructed for a RemoteWorkFile.

Here is a complete example:

using System;
using System.IO;
using System.Linq;
using System.Threading.Tasks;
using Accusoft.PrizmDocServer;
using Accusoft.PrizmDocServer.Conversion;

namespace Demos
{
    class Program
    {
        static void Main(string[] args)
        {
            MainAsync().GetAwaiter().GetResult();
        }

        static async Task MainAsync()
        {
            var prizmDocServer = new PrizmDocServerClient(/* your connection info */);

            // Extract the first page as an intermediate PDF. We won't ever bother
            // downloading this from PrizmDoc Server.
            var tempFirstPagePdf = await prizmDocServer.ConvertToPdfAsync(new ConversionSourceDocument("project-proposal.docx", pages: "1"));

            // Convert the PDF to PNGs, specifying a max width and height. We'll get
            // back a collection of results, one per page. In our case, there is only
            // one page.
            IEnumerable<ConversionResult> thumbnailPngs = await prizmDocServer.ConvertAsync(new ConversionSourceDocument(tempFirstPagePdf.RemoteWorkFile), new DestinationOptions(DestinationFileFormat.Png)
            {
                PngOptions = new PngDestinationOptions() {
                    MaxWidth = "512px",
                    MaxHeight = "512px"
                }
            });

            // Save the single result.
            await thumbnailPngs.Single().RemoteWorkFile.SaveAsync("thumbnail.png");
        }
    }
}