bines multiple PDF files into a single PDF file. Allows specifying which pages of the source files to combine.</p>
<p>Sample Usage:</p>
<pre class="prettyprint">
<code>

 const credentials = PDFServicesSdk.Credentials.servicePrincipalCredentialsBuilder()
           .withClientId("PDF_SERVICES_CLIENT_ID")
           .withClientSecret("PDF_SERVICES_CLIENT_SECRET")
           .build(),
       executionContext = PDFServicesSdk.ExecutionContext.create(credentials),
       CombineFiles = PDFServicesSdk.CombineFil