When merging, only the widgets are copied but not their fields. This can lead to ArgumentNullException when exporting the document. Implement copying the fields and consider cases which include collision of names of the fields.

Workaround:
Repair the generated document using the following code:
foreach (Widget widget in this.pdfDocument.Annotations.Where(annot => annot.Type == AnnotationType.Widget))
{
    if (!this.pdfDocument.AcroForm.FormFields.Contains(widget.Field.Name))
    {
        this.pdfDocument.AcroForm.FormFields.Add(widget.Field);
    }
}
In case of Name collision, you can use the attached project or the attached project to the following feedback item to rename the duplicate fields: Provide a way to rename FormFields.

When opened in Adobe Reader it says that the file "claims compliance". However, when verifying the compliance with some validation tools there seem to be some issues mainly related but not limited to fonts. 

This is reproducible with specific PDF files which use custom Encoding for the fonts of the field widgets. 

WORKAROUND: Change the font of VariableContentWidgets before editing the field value. You should additionally call RecalculateContent() method of these widgets if the value of their corresponding fields is not edited. The following method may be used for changing the font of all existing widgets in the document:

private static void FixEncodingIssues(RadFixedDocument document)
{
    foreach(Annotation annotation in document.Annotations)
    {
        VariableContentWidget widget = annotation as VariableContentWidget;

        if(widget != null)
        {
            widget.TextProperties.Font = FontsRepository.Helvetica;
        }
    }
}

After signing a document using the PdfProcessing library and the document is loaded in Adobe Acrobat an error is shown when the signature widget is clicked:
Error during signature verification.  

Adobe Acrobat error.
Expected a dict object.

When importing color space defined as an external resource name, a NotSupportedColorSpaceException: 'CS0 color space is not supported.' is thrown.

Although Lab color space is currently unsupported, the provider should not throw exceptions that break the whole file import.

When creating a GradientStop, an alpha channel of the color could be applied. However, this setting is not respected it the result document and the gradient is with full opacity.

Steps to reproduce:
1. Create a gradient with an alpha channel:

RadFixedDocument document = new RadFixedDocument();
RadFixedPage page = document.Pages.AddPage();
FixedContentEditor containerEditor = new FixedContentEditor(page);

LinearGradient linearGradient = new LinearGradient(new Point(0, 0), new Point(30, 30));
linearGradient.GradientStops.Add(new GradientStop(new RgbColor(10, 0, 207, 0), 0));
linearGradient.GradientStops.Add(new GradientStop(new RgbColor(10, 0, 102, 204), 1));

containerEditor.GraphicProperties.FillColor = linearGradient;
containerEditor.DrawRectangle(new Rect(10, 10, 48, 29));

2. Export the document to PDF

Observed: The alpha channel is not respected and the gradient is with full opacity

Currently this exception crashes the whole PDF document import. Instead we should simply skip the unsupported Action and import the rest of the PDF content correctly.

For example, importing URI Action with invalid mailto URL scheme - mailto:***@***.**(E-mail), throws UriFormatException: 'Invalid URI: The hostname could not be parsed.'

When a TrueType font is defined, the mapping of character codes to glyph indices depends on the built-in cmap table mappings defined in the font and the Encoding property defined in the PDF dictionary.

However, the current implementation maps all characters with cmap tables for Microsoft Symbolic and Macintosh Roman, which causes incorrect mapping results, e.g. space characters are mapped to an Ê glyph.

The issue is also described in the following public item: TryGetCharCode for OpenTypeFont uses wrong cmap and returns wrong charcode.

Workaround: Change the font  of the TextBoxField's widget appearance:
foreach (var widget in field.Widgets)
{
    widget.TextProperties.Font = FontsRepository.Helvetica;
}

The exception is thrown when CIDSet is imported.

The EI keyword defines an operator for ending the image data. When the stream contains the same sequence, the parser treats that as an end of the image data. As a result, the image and the following content cannot be properly parsed and there is missing content when the document is visualized.

By specification, the InteractiveForm fields can have the same name if they are descendants of a common ancestor. Such fields are different representations of the same underlying field; they should differ only in properties that specify their visual appearance. When such a document is imported an ArgumentException: 'An item with the same key has already been added.' is thrown.

Exporting document with a missing image is caused by handled Exception on import for DecodeParms containing null or stream object. Currently, PdfProcessing supports only decode parameters containing simple types. The case when some dictionary value is null or stream object should be implemented.

Another case is when the whole dictionary/stream is null. In this case, an ArgumentNullException is thrown.

The issue may be reproduced by opening the attached PDF in Adobe Reader. Although the viewer initially shows the characters correctly, when you start typing in the TextBox, the umlaut/diacritics characters get corrupted. In other PDF viewers, the umlaut characters are handled correctly, so the issue seems to related to concrete Adobe Reader encoding handling implementation. The diacritic characters are handled incorrectly in other viewers as well (e.g. Chrome).

When merging or splitting files that contain the "159 '\u009f'" char, ArgumentException("The encoding is not supported.") is thrown.

This issue can also result in ArgumentException in client applications with the message: currentIndirectObject should be null.

Workaround:

Use PdfFormatProvider or reflection to register the char (check the comments).

Trying to clone the Signature of a SignatureField leads to InvalidOperationException as the FieldName of the cloned signature is already set.

The exception is thrown with the message "Password is not correct" even when the user password is correct. This issue occurs for specific encryption algorithm parameters only.

InvalidOperationException is thrown when exporting font that is available but not used.

The stack trace is as follows:
   at System.Linq.Enumerable.Max(IEnumerable`1 source)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Elements.Fonts.Cid.CidSet.CopyPropertiesFrom(IPdfExportContext context, FontBase font)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Elements.Fonts.CidFontDescriptor.CalculateCidSet(IPdfExportContext context, CidFontBase font)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Elements.Fonts.CidFontDescriptor.<>c__DisplayClass34.<CopyPropertiesFrom>b__30()
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Utilities.PdfObjectsExtensions.ToPrimitive[P,T](PdfProperty`1 pdfProperty, Func`2 convertToPrimitive, Func`1 getDefaultValue)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Elements.Fonts.CidFontDescriptor.CopyPropertiesFrom(IPdfExportContext context, FontBase font)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Elements.Fonts.CidFontObject.CopyPropertiesFromOverride(IPdfExportContext context, FontBase font)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Elements.Fonts.CidFontObject.CopyPropertiesFrom(IPdfExportContext context, FontBase font)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Elements.Fonts.Type0FontObject.CopyPropertiesFromOverride(IPdfExportContext context, FontBase font)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Export.PdfExporter.WriteFontsFromContext(PdfWriter writer, IPdfExportContext context)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Export.PdfExporter.Export(IRadFixedDocumentExportContext context, Stream output)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.PdfFormatProvider.ExportOverride(RadFixedDocument document, Stream output)
   at Telerik.Windows.Documents.Common.FormatProviders.FormatProviderBase`1.Export(T document, Stream output)

The checkbox state is not correctly imported when the value is not specified