Update README.md

Author: AnnaVekhina

README.md

@@ -8,7 +8,7 @@
 * [Program.cs](./CS/PdfDocumentProcessor/Program.cs) (VB: [Program.vb](./VB/PdfDocumentProcessor/Program.vb))
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-# How to Apply Multiple Signatures
+# PDF Document API - Apply Multiple Signatures
 
 The **PDF Document API** allows you to apply multiple PKCS#7 signatures with X.509 certificates.