[Solved] PdfFormatProvider.Import fails with Cryptography_UnknownHashAlgorithm, MD5 when importing a password-protected RC4 encrypted PDF on .NET 10

[Vaibhav]

Product

Telerik Document Processing – PdfProcessing

Environment
Telerik.Documents.Fixed: 2026.2.723
Telerik.UI.for.Blazor: 14.0.0
.NET: 10.0
Blazor WebAssembly
Windows 11


Description
I'm implementing support for previewing password-protected PDFs in a Blazor application.

The workflow is:

User opens a password-protected PDF.
Application prompts for the password.
Password is supplied through PdfImportSettings.UserPasswordNeeded.
PdfFormatProvider.Import() is called.
The import fails with:
Cryptography_UnknownHashAlgorithm, MD5

The password is correct.

The same PDF opens successfully in Adobe Acrobat using the same password.

PDF Security

Adobe Acrobat reports:

Security Method: Password Security

Document Open Password: Yes
Permissions Password: No

Encryption Level:
128-bit RC4

Code used
using Telerik.Windows.Documents.Fixed.FormatProviders.Pdf;
using Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Import;

var provider = new PdfFormatProvider();

var settings = new PdfImportSettings();

settings.UserPasswordNeeded += (s, e) =>
{
    e.Password = "samplefiles";
};

settings.OwnerPasswordNeeded += (s, e) =>
{
    e.Password = "samplefiles";
};

provider.ImportSettings = settings;

using var stream = new MemoryStream(pdfBytes);

var document = provider.Import(
    stream,
    TimeSpan.FromSeconds(30));


Expected Result

The PDF should be imported successfully and the returned RadFixedDocument should be available for rendering/export.

Actual Result

provider.Import() throws:

Cryptography_UnknownHashAlgorithm, MD5

before the document is imported.

Additional Information
The password is verified by Adobe Acrobat and opens the document successfully.
The exception occurs even when the correct password is provided.
The PDF uses 128-bit RC4 encryption.
We would like to know whether:
RC4/MD5 encrypted PDFs are supported by Telerik.Documents.Fixed,
this is a known issue with .NET 10,
or whether there is a recommended workaround.

[Yoan]

This discussion has been moved to a private support ticket to allow the secure sharing of files and to continue the investigation.

A similar CryptographicException affecting Blazor WASM, related to MD5 availability, was reported in the past and was resolved in 2026.2.519 (2026 Q2) - PdfProcessing: A CryptographicException because MD5 not available on Blazor WASM. Based on the reported version, this does not appear to be the same issue, and further investigation is required to determine the root cause.

The investigation will continue in the associated support ticket, and this thread will be updated if any findings are applicable to other users.