MHT to PDF conversion fails with "An item with the same key has already been added. Key: font-size"

Aspose.PDF Cloud Product Family
1

Calling PdfApi.GetMhtInStorageToPdf() via the .NET SDK. For a broad set of inputs, it intermittently fails with an “internalError” code.

Sample:

{
    "RequestId": "06952c9f715605a885bb95da55d5e33d",
    "Error": {
        "Code": "internalError",
        "Message": "An item with the same key has already been added. Key: font-size",
        "Description": "Operation Failed. Internal error.",
        "DateTime": "2026-09-29T01:28:44.3682834Z",
        "InnerError": null
    }
}

Can supply example inputs if required.

2

Hi, @contactslaw
Can you please share your sample document and code to reproduce the issue? We will further proceed to assist you accordingly.

3

139802 - Email from B Smith to B Smith - Example email.zip (23.9 KB)

The above sample produced the following error (similar but different dictionary key in error message):

{
    "RequestId": "e7e8b763b05e4eb77bdff5d8191cad67",
    "Error": {
        "Code": "internalError",
        "Message": "An item with the same key has already been added. Key: panose-1",
        "Description": "Operation Failed. Internal error.",
        "DateTime": "2026-09-29T08:00:49.5077751Z",
        "InnerError": null
    }
}

Code to reproduce the issue:

string srcPath = "4je50mu5.mht";	// random filename, different on each call

var client = new PdfApi(clientSecret, clientId);

using (var src = File.OpenRead("example.mht")) {
    await client.UploadFileAsync(srcPath, src);
}

await client.GetMhtInStorageToPdfAsync(srcPath);	// ApiException is thrown here
4

Hi, @contactslaw Im report issue and logged the following ticket in our issue tracking system for further investigation and rectification. We will notify you as soon as these issues are resolved.

PDFCLOUD-5757 MHT to PDF conversion fails