Added new kb article pdfviewer-upload-controls-visibility (#2739)

* Added new kb article pdfviewer-upload-controls-visibility

* chore: polish example and update article content for better seo

* chore: mention dropzone

---------

Co-authored-by: KB Bot <kb-bot@telerik.com>
Co-authored-by: Tsvetomir Hristov <106250052+Tsvetomir-Hr@users.noreply.github.com>

Author: 3 people

knowledge-base/pdfviewer-upload-controls-visibility.md

@@ -0,0 +1,68 @@
+---
+title: How to Hide Upload Component in TelerikPdfViewer
+description: Learn how to hide the Upload component in TelerikPdfViewer when loading a PDF file.
+type: how-to
+page_title: How to Hide Upload Component in TelerikPdfViewer
+slug: pdfviewer-kb-hide-upload
+tags: pdfviewer, blazor, upload, visibility, enableloadercontainer, hide, dropzone
+res_type: kb
+ticketid: 1675214
+---
+
+## Environment
+
+<table>
+	<tbody>
+		<tr>
+			<td>Product</td>
+			<td>PdfViewer for Blazor</td>
+		</tr>
+	</tbody>
+</table>
+
+## Description
+
+When using the [TelerikPdfViewer](https://docs.telerik.com/blazor-ui/components/pdfviewer/overview) for Blazor, upload controls may still be visible while a PDF file is loading, even if the `EnableLoaderContainer` parameter is set to `false`. 
+
+This knowledge base article also answers the following questions:
+
+- How to prevent interaction with Upload component while a PDF is loading in TelerikPdfViewer?
+- How to hide Upload and DropZone components in TelerikPdfViewer until the PDF file is fully loaded?
+- How to use custom CSS with TelerikPdfViewer to hide Upload component?
+
+## Solution
+
+To control the visibility of Upload component and its dropzone in the `TelerikPdfViewer` while a PDF is loading, apply custom CSS to hide the upload controls. To achieve that, use the [`OnOpen`](slug://components/pdfviewer/events#onopen) event to apply a CSS class with the required styles that hide the controls until the PDF file is loaded successfully.
+
+````RAZOR
+<TelerikPdfViewer Data="@PdfSource"
+                  Height="600px"
+                  EnableLoaderContainer="false"
+                  OnOpen="@OnPdfOpen"
+                  Class="@PdfClass">
+</TelerikPdfViewer>
+<style>
+    .hide-pdf-upload .k-external-dropzone {
+        display: none;
+    }
+
+    .hide-pdf-upload .k-upload {
+        display: none;
+    }
+</style>
+@code {
+    private byte[] PdfSource { get; set; }
+    private string PdfClass { get; set; } = "";
+
+    private async Task OnPdfOpen(PdfViewerOpenEventArgs args)
+    {
+        //hide Upload component
+        PdfClass = "hide-pdf-upload";
+    }
+}
+````
+
+## See Also
+
+- [TelerikPdfViewer Overview](slug://components/pdfviewer/overview)
+- [TelerikPdfViewer Events](slug://components/pdfviewer/events)