Biblioteca para editar archivos pdf con C# en UWP

Syncfusion Essential PDF para UWP también es compatible con .NET Core. Pruebe este código de muestra .

            //Loading Pdf and image to stream

         Stream jpegImage = typeof(MainPage).GetTypeInfo().Assembly.GetManifestResourceStream("templateForm.DataUWP.images.png");
        Stream  docStream = typeof(MainPage).GetTypeInfo().Assembly.GetManifestResourceStream("templateForm.DataUWP.Form.pdf");


        PdfLoadedDocument loadedDocument = new PdfLoadedDocument(docStream);

        //Draw image 

        PdfImage img = new PdfBitmap(jpegImage);

        loadedDocument.Pages[0].Graphics.DrawImage(img, new PointF(380, 90), new SizeF(100, 100));

        //Get the loaded form.

        PdfLoadedForm loadedForm = loadedDocument.Form;

        PdfLoadedFormFieldCollection fieldCollection = loadedForm.Fields as PdfLoadedFormFieldCollection;

        PdfLoadedField loadedField = null;

        // Get the field using TryGetField Method and fill it.


        if (fieldCollection.TryGetField("name", out loadedField))

        {

            (loadedField as PdfLoadedTextBoxField).Text = "John";

        }

        //Save the modified document.
        MemoryStream streamOut = new MemoryStream();
        loadedDocument.Save(streamOut);

        //Close the document

        loadedDocument.Close(true);

        //Save document to file
        Save(streamOut, "sample.pdf");

La biblioteca XFINIUM.PDF es compatible con Windows 10 UWP.
Su plantilla no incluye ningún campo, así que la modifiqué. El código para llenar el formulario se ve así:

private Assembly assembly = typeof(MainPage).GetTypeInfo().Assembly;

private async void btnFillDocumentTemplate_Click(object sender, RoutedEventArgs e)
{
    Stream pdfStream = assembly.GetManifestResourceStream("UWP_FillDocumentTemplate.ModelReleaseTemplate.pdf");
    PdfFixedDocument document = new PdfFixedDocument(pdfStream);
    pdfStream.Dispose();

    // Fill photographer info
    document.Form.Fields["PhotographerName"].Value = "John Doe";
    document.Form.Fields["PhotographerDateSigned"].Value = "09/03/2017";
    document.Form.Fields["PhotographerShootDate"].Value = "08/03/2017";
    document.Form.Fields["PhotographerShootCountry"].Value = "Italy";
    document.Form.Fields["PhotographerShootDescription"].Value = "Tuscany";
    // Draw photographer signature
    DrawImageAtFieldLocation(document.Form.Fields["PhotographerSignature"].Widgets[0], "PhotographerSignature.png");

    // Fill model info
    document.Form.Fields["ModelName"].Value = "Jane Doe";
    document.Form.Fields["ModelDOB"].Value = "01/01/1980";
    document.Form.Fields["ModelGender"].Value = "Male";
    document.Form.Fields["ModelAddress1"].Value = "via Romana no 1";
    document.Form.Fields["ModelCity"].Value = "Rome";
    document.Form.Fields["ModelState"].Value = "Rome";
    document.Form.Fields["ModelCountry"].Value = "Italy";
    document.Form.Fields["ModelZip"].Value = "12345";
    document.Form.Fields["ModelPhone"].Value = "0123456789";
    document.Form.Fields["ModelEmail"].Value = "jane.doe@nomail.com";
    document.Form.Fields["ModelDateSigned"].Value = "09/03/2017";
    document.Form.Fields["ModelParentName"].Value = "Parent Jane Doe";
    // Draw model signature
    DrawImageAtFieldLocation(document.Form.Fields["ModelSignature"].Widgets[0], "ModelSignature.png");
    // Draw model visual
    DrawImageAtFieldLocation(document.Form.Fields["ModelVisualReference"].Widgets[0], "XFINIUM.PDF.png");

    // Fill ethnicity
    (document.Form.Fields["EthnicityAsian"] as PdfCheckBoxField).Checked = true;

    // Fill witness info
    document.Form.Fields["WitnessName"].Value = "Witness John Doe";
    document.Form.Fields["WitnessDateSigned"].Value = "09/03/2017";
    // Draw photographer signature
    DrawImageAtFieldLocation(document.Form.Fields["WitnessSignature"].Widgets[0], "WitnessSignature.png");

    // If you want to prevent changes to filled data, you can flatten the form fields.
    document.Form.FlattenFields();

    // Save the filled form
    FileSavePicker fileSavePicker = new FileSavePicker();
    fileSavePicker.FileTypeChoices.Add("PDF files", new List<string>() { ".pdf" });
    fileSavePicker.SuggestedFileName = "ModelReleaseFilled";

    var outputFile = await fileSavePicker.PickSaveFileAsync();
    if (outputFile != null)
    {
        var destPdfStream = await outputFile.OpenAsync(FileAccessMode.ReadWrite);
        using (Stream stm = destPdfStream.AsStream())
        {
            document.Save(stm);
            await stm.FlushAsync();
        }
        destPdfStream.Dispose();
    }
}

private void DrawImageAtFieldLocation(PdfFieldWidget fieldWidget, string imageName)
{
    Stream imageStream = assembly.GetManifestResourceStream("UWP_FillDocumentTemplate." + imageName);
    PdfPngImage image = new PdfPngImage(imageStream);
    PdfVisualRectangle fieldRect = fieldWidget.VisualRectangle;
    // Draw the image on the page where the field widget is located.
    fieldWidget.Page.Graphics.DrawImage(image,
        fieldRect.Left, fieldRect.Top, fieldRect.Width, fieldRect.Height);

    imageStream.Dispose();
}

Puede descargar el formulario completo y el proyecto de muestra .
Descargo de responsabilidad: trabajo para la empresa que desarrolla esta biblioteca.