<TelerikButton OnClick="@OnOpenToggle">Toggle Open Buttons</TelerikButton>

<TelerikPdfViewer Data="@PdfSource"
                  Class="@HideOpenClass"
                  Height="400px" />

<style>
    .hide-open .k-blank-page,
    .hide-open .k-button:has(.k-i-folder-open) {
        display: none;
    }
</style>

@code {
    private byte[] PdfSource { get; set; }

    private string HideOpenClass { get; set; } = string.Empty;

    private async Task OnOpenToggle()
    {
        string _hideOpenClass = "hide-open";

        HideOpenClass = HideOpenClass == _hideOpenClass ? string.Empty : _hideOpenClass;
    }
}