Replaced static upload message in `CreateEnvelopeWizardPopup.razor` with a new `PdfFileDropZone` component to enhance user experience. The component supports drag-and-drop functionality, file selection, and dynamic states (e.g., disabled, drag-active).
Introduced `PdfFileDropZone.razor` with customizable parameters such as `Disabled`, `HasDocument`, `UploadText`, and `DragDropHintText`. Added event handling for drag-and-drop interactions and file selection.
Updated `sender-page.css` to include styles for the new component, ensuring seamless integration with the existing layout. Adjusted styles for hover effects, drag-active state, and disabled state.
These changes improve usability and make PDF uploads more intuitive.
