library(shiny)

ui <- shinyUI(fluidPage(

  titlePanel("Testing File upload"),

  sidebarLayout(
    sidebarPanel(
      fileInput('file_input', 'upload file ( . pdf format only)', accept = c('.pdf'))
    ),

    mainPanel(
      uiOutput("pdfview")
    )
  )
))

server <- shinyServer(function(input, output) {

  observe({
    req(input$file_input)



     file.copy(input$file_input$datapath,"www", overwrite = T)



  output$pdfview <- renderUI({
    tags$iframe(style="height:600px; width:100%", src="0.pdf")
  })

  })

})

shinyApp(ui = ui, server = server)