1ed873fc84
Introduced a new `PdfSigningService` for digitally signing PDFs using a PFX certificate and DevExpress's `PdfDocumentSigner`. Updated `Program.cs` to register the service and added a new configuration section `PdfSigning` in `appsettings.json` for certificate management. Added a Razor Page `TestSignature.cshtml` and its page model `TestSignature.cshtml.cs` to provide a user interface for testing PDF signing. The page includes file upload, signature validation, and result display functionality. Implemented supporting classes `PdfSigningOptions` for signature customization and `SignatureInformation` for extracting and displaying signature details, including signer name, location, and certificate validity.