How to return a PDF from a Web API application

Some Server side code to return PDF (Web Api).

[HttpGet]
[Route("documents/{docid}")]
public HttpResponseMessage Display(string docid) {
    HttpResponseMessage response = Request.CreateResponse(HttpStatusCode.BadRequest);
    var documents = reader.GetDocument(docid);
    if (documents != null && documents.Length == 1) {
        var document = documents[0];
        docid = document.docid;
        byte[] buffer = new byte[0];
        //generate pdf document
        MemoryStream memoryStream = new MemoryStream();
        MyPDFGenerator.New().PrintToStream(document, memoryStream);
        //get buffer
        buffer = memoryStream.ToArray();
        //content length for use in header
        var contentLength = buffer.Length;
        //200
        //successful
        var statuscode = HttpStatusCode.OK;
        response = Request.CreateResponse(statuscode);
        response.Content = new StreamContent(new MemoryStream(buffer));
        response.Content.Headers.ContentType = new MediaTypeHeaderValue("application/pdf");
        response.Content.Headers.ContentLength = contentLength;
        ContentDispositionHeaderValue contentDisposition = null;
        if (ContentDispositionHeaderValue.TryParse("inline; filename=" + document.Name + ".pdf", out contentDisposition)) {
            response.Content.Headers.ContentDisposition = contentDisposition;
        }
    } else {
        var statuscode = HttpStatusCode.NotFound;
        var message = String.Format("Unable to find resource. Resource \"{0}\" may not exist.", docid);
        var responseData = responseDataFactory.CreateWithOnlyMetadata(statuscode, message);
        response = Request.CreateResponse((HttpStatusCode)responseData.meta.code, responseData);
    }
    return response;
}

On my a View you could do something like this

<a href="api/documents/1234" target = "_blank" class = "btn btn-success" >View document</a>

which will call the web api and open the PDF document in a new tab in the browser.

Here is how i basically do the same thing but from a MVC controller

// NOTE: Original return type: FileContentResult, Changed to ActionResult to allow for error results
[Route("{docid}/Label")]
public ActionResult Label(Guid docid) {
    var timestamp = DateTime.Now;
    var shipment = objectFactory.Create<Document>();
    if (docid!= Guid.Empty) {
        var documents = reader.GetDocuments(docid);
        if (documents.Length > 0)
            document = documents[0];

            MemoryStream memoryStream = new MemoryStream();
            var printer = MyPDFGenerator.New();
            printer.PrintToStream(document, memoryStream);

            Response.AppendHeader("Content-Disposition", "inline; filename=" + timestamp.ToString("yyyyMMddHHmmss") + ".pdf");
            return File(memoryStream.ToArray(), "application/pdf");
        } else {
            return this.RedirectToAction(c => c.Details(id));
        }
    }
    return this.RedirectToAction(c => c.Index(null, null));
}

Hope this helps

I needed to return a pdf file from a .NET core 3.1 web api, and found this excellent article:

https://codeburst.io/download-files-using-web-api-ae1d1025f0a9

Basically, you call:

var bytes = await System.IO.File.ReadAllBytesAsync(pathFileName);
return File(bytes, "application/pdf", Path.GetFileName(pathFileName));

Whole code is:

using Microsoft.AspNetCore.Mvc;
using System.IO;

using Reportman.Drawing;
using Reportman.Reporting;
using System.Text;
using System.Threading.Tasks;

[Route("api/[controller]")]
[ApiController]
public class PdfController : ControllerBase
{
    [HttpGet]
    [Route("ot/{idOT}")]
    public async Task<ActionResult> OT(string idOT)
    {
        Report rp = new Report();
        rp.LoadFromFile("ot-net.rep"); // File created with Reportman designer
        rp.ConvertToDotNet();

        // FixReport
        rp.AsyncExecution = false;
        PrintOutPDF printpdf = new PrintOutPDF();

        // Perform the conversion from one encoding to the other.
        byte[] unicodeBytes = Encoding.Convert(Encoding.ASCII, Encoding.Unicode, Encoding.ASCII.GetBytes($"Orden de trabajo {idOT}"));
        string unicodeString = new string(Encoding.Unicode.GetChars(unicodeBytes));
        // todo: convert to unicode
        // e = Encoding.GetEncoding(unicodeString);
        // System.Diagnostics.Trace.WriteLine(e);
        if (rp.Params.Count > 0)
        {
            rp.Params[0].Value = unicodeString;
        }

        printpdf.FileName = $"ot-{idOT}.pdf";
        printpdf.Compressed = false;

        if (printpdf.Print(rp.MetaFile))
        {
            // Download Files using Web API. Changhui Xu. https://codeburst.io/download-files-using-web-api-ae1d1025f0a9
            var bytes = await System.IO.File.ReadAllBytesAsync(printpdf.FileName);
            return File(bytes, "application/pdf", Path.GetFileName(printpdf.FileName));
        }

        return null;
    }

Call to this API looks like: https://localhost:44387/api/pdf/ot/7

Reportman is a pdf generator you can found at: https://reportman.sourceforge.io/

Enjoy!