Facing an issue with DOC/DOCX to HTML conversion

[ceipalAdmin]

1)We are facing an issue with DOC/DOCX to HTML conversion for some files.
The conversion is failing with the error: "Input string was not in a correct format" while loading the document through Spire.Doc.
2) using (var doc = new Spire.Doc.Document())
{
doc.LoadFromFile(inputFile);
doc.SaveToFile(tempPdfFile, Spire.Doc.FileFormat.PDF);
}
3)Spire.Pdf.NetCore 7.12.1
4)Windows-10 64 bit
5)Console.Application(.Net 5.0)

[Nina.Tang]

Hi,

Thanks for your inquiry.
I tested your document using Spire.Doc but was unable to reproduce the issue you described.

I also noticed that you provided the version information for Spire.PDF（Spire.Pdf.NetCore 7.12.1）. Please kindly note that converting Word to PDF/HTML is a feature of the Spire.Doc product. Could you please confirm which specific version of Spire.Doc you are currently using?

Upon checking your purchase record, I can confirm that you are entitled to use versions released up to 2026/1/10. This includes Spire.Docfor .NET Standard v14.1.3 (released on 2026/1/9). Please download this version from NuGet and verify if the issue persists.

Sincerely,
Nina
E-iceblue support team

[ceipalAdmin]

Hi,

Thank you for your response.

We purchased a license for Spire.Office, which should cover all related document conversion components, including Word to PDF/HTML conversions.

Based on your suggestion, we installed Spire.Doc and tested the conversion again. However, the generated output still contains the evaluation watermark.

Additionally, when Spire.Doc is not installed, the conversion process throws the following error:
"Input string was not in a correct format."

Could you please help us understand:

Whether the existing Spire.Office license needs to be applied separately for Spire.Doc
Whether any additional configuration or steps are required to remove the evaluation watermark
Whether the above error is related to licensing or package compatibility

We will also test with Spire.Doc for .NET Standard v14.1.3 as recommended and update you with the results.

Looking forward to your guidance.

Thanks

[Nina.Tang]

Hi,

Thanks for your feedback.
Regarding the error message 'Input string was not in a correct format.' that you encountered, this is caused by using the PDF component to load a Word document. The mismatched file format triggers this exception.
Additionally, concerning the issue where the watermark persists even after updating Spire.Doc, we need to look into a few more details to pinpoint the exact cause:
1. Which specific version of Spire.Doc are you currently using?
2. How are you applying the license in your code?
3. Could you also please provide your license Order Number? This will allow us to verify the license details on our end.

Sincerely,
Nina
E-iceblue support team

[ceipalAdmin]

Hi Nina,

Thank you for your response.

Please find the requested details below:

We are currently using the latest stable version of Spire.Doc: 14.4.9.
We are applying the license in our code as follows:
private const string LICENSE_KEY = licenseky; // Store license key as constant

private void LoadLicenses()
{
Spire.License.LicenseProvider.SetLicenseKey(LICENSE_KEY);
Spire.License.LicenseProvider.LoadLicense();
}
LoadLicenses();
// Convert DOC -> temp PDF so the downstream PDF->HTML produces SVG/page-based output
using (var doc = new Spire.Doc.Document())
{
doc.LoadFromFile(inputFile);
doc.SaveToFile(tempPdfFile, Spire.Doc.FileFormat.PDF);
}
Regarding the Order Number is 00015746.

Please let me know if you need any additional information from our side.

Sincerely,
Ceipal

[Nina.Tang]

Dear Ceipal,

Thank you for providing the detailed information. Based on what you've shared, we have identified the root causes of the issue. Here is a breakdown of the situation and how to resolve it:

1. You purchased the Spire.Office for .NET Developer Small Business on January 10, 2025. This subscription covers versions released up until January 10, 2026.
The version Spire.Doc v14.4.9 you upgraded, was released on April 28, 2026, which falls outside your authorized coverage period. This is why the watermark is appearing.

2. Starting from Spire.Doc v11.5.6, we adjusted the namespace for applying licenses. You need to update your code to use the new namespace:

Code: Select all

Spire.Doc.License.LicenseProvider.SetLicenseKey("your license key")

instead of the old one:

Code: Select all

Spire.License.LicenseProvider.SetLicenseKey("your license key")

For more details, please refer to this document: https://www.e-iceblue.com/Tutorials/Licensing/Licensing.html#Apply_by_Key

Solution:
To fix this, please follow these steps:
1. Remove all Spire DLLs from your project.
2. Then reinstall Spire.Office v10.12.0. This version was released on December 31, 2025, and is the latest version covered by your current license.
3. Apply your license key using the new namespace mentioned above.

Important Note:
If you have followed these steps and the watermark still persists, there is another critical factor to consider. Your license type is Developer Small Business, which permits usage by 1 developer and 1 deployment location, each identified by a unique MAC address. Your license may have exceeded the allowed usage limit, and you have most likely applied the license on multiple machines.

Anyway, please proceed with the steps above first. If the watermark persists, let me know and I will provide further guidance.

Sincerely,
Nina
E-iceblue support team