PdfConverter ASP.NET Core Integration Guide

This guide shows how to integrate PdfConverter into an ASP.NET Core application to expose Visio-to-PDF conversion as an HTTP endpoint.

Prerequisites

Aspose.Diagram for .NET (version 26.4.0 or later)
ASP.NET Core 6.0 or later
License applied at application startup (see Step 1)

Step 1: Apply License at Startup

Apply your Aspose license once in Program.cs before the application starts processing requests:

using Aspose.Diagram;

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

var metered = new Metered();
metered.SetMeteredKey("publicKey", "privateKey");

app.Run();

Step 2: Create a PDF Export Endpoint (Stream-Based)

Use stream-based conversion to avoid writing temporary files to disk:

using System.IO;
using Aspose.Diagram.LowCode;
using Microsoft.AspNetCore.Mvc;

[ApiController]
[Route("api/diagram")]
public class PdfConverterController : ControllerBase
{
    [HttpPost("export-pdf")]
    public IActionResult ExportToPdf(IFormFile visioFile)
    {
        if (visioFile == null || visioFile.Length == 0)
            return BadRequest("No file uploaded.");

        using var outputStream = new MemoryStream();

        var loadOptions = new LowCodeLoadOptions();
        loadOptions.InputStream = visioFile.OpenReadStream();

        var saveOptions = new LowCodePdfSaveOptions();
        saveOptions.OutputStream = outputStream;

        PdfConverter.Process(loadOptions, saveOptions);

        string fileName = Path.ChangeExtension(visioFile.FileName, ".pdf");
        return File(outputStream.ToArray(), "application/pdf", fileName);
    }
}

Step 3: Add Error Handling

Wrap the conversion in a try/catch to return appropriate HTTP status codes:

using System;
using System.IO;
using Aspose.Diagram.LowCode;
using Microsoft.AspNetCore.Mvc;

[HttpPost("export-pdf")]
public IActionResult ExportToPdf(IFormFile visioFile)
{
    if (visioFile == null || visioFile.Length == 0)
        return BadRequest("No file uploaded.");

    string tempInput = Path.GetTempFileName() + ".vsdx";
    try
    {
        using (var stream = System.IO.File.Create(tempInput))
            visioFile.CopyTo(stream);

        var loadOptions = new LowCodeLoadOptions();
        loadOptions.InputFile = tempInput;

        var saveOptions = new LowCodePdfSaveOptions();
        var ms = new MemoryStream();
        saveOptions.OutputStream = ms;

        PdfConverter.Process(loadOptions, saveOptions);

        string fileName = Path.ChangeExtension(visioFile.FileName, ".pdf");
        return File(ms.ToArray(), "application/pdf", fileName);
    }
    catch (Exception ex)
    {
        return StatusCode(500, $"PDF export failed: {ex.Message}");
    }
    finally
    {
        if (System.IO.File.Exists(tempInput))
            System.IO.File.Delete(tempInput);
    }
}

Troubleshooting

Problem	Likely Cause	Fix
Evaluation watermark in PDF	License not applied at startup	Apply `metered.SetMeteredKey()` in `Program.cs` before `app.Run()`
Upload rejected with 413	Request body size limit exceeded	Configure `MaxRequestBodySize` for large Visio files
Empty PDF returned	Input stream not readable	Ensure `visioFile.OpenReadStream()` is called after upload completes
Temp file not deleted on error	Missing `finally` block	Always delete temp files in a `finally` block