AccessViolationException During Form Processing (c0000005)

While processing PDF forms, IronPDF can throw an intermittent native AccessViolationException (code c0000005) that does not reproduce reliably, even on the same input file. It shows up most often when you access PdfDocument.Form and during PdfDocument.Flatten and PdfDocument.Merge.

AccessViolationException (0xc0000005)
bad conversion while widening narrow string

The crash comes from the interaction between native form-field handles and managed object lifetime. If the PdfDocument is garbage-collected or disposed while native form operations are still in flight, the native layer accesses memory that has already been freed, which produces the access violation.

The repeated "bad conversion while widening narrow string" warnings, along with warnings about removing form-field annotations during flattening, are a separate and benign symptom. They come from decoding internal AcroForm field strings and metadata that contain Japanese or multibyte characters in a given PDF. They do not indicate a problem with Japanese or Unicode support in general, nor with Japanese UNC file paths.

Using doc As IronPdf.PdfDocument = IronPdf.PdfDocument.FromFile(tempPdfPath)
    For Each field In doc.Form
        ' Your form field processing here
    Next
    GC.KeepAlive(doc)
End Using

Using doc As IronPdf.PdfDocument = IronPdf.PdfDocument.FromFile(tempPdfPath)
    For Each field In doc.Form
        ' Your form field processing here
    Next
    GC.KeepAlive(doc)
End Using