Outputting Shiny (non-ggplot) plot to PDF

Is there a method to output (UI end) Shiny plots to PDF for the app user to download? I've tried various methods similar to those involving ggplot, but it seems downloadHandler can't operate in this way. For example the following just produces broken PDF's that don't open.

Solved. The plot should be saved locally with pdf(), not the screen device (as with dev.copy2pdf). Here's a working example: shiny::runGist('d8d4a14542c0b9d32786'). For a nice basic model try:

server.R

library(shiny)
shinyServer(
    function(input, output) {

        plotInput <- reactive({
            if(input$returnpdf){
                pdf("plot.pdf", width=as.numeric(input$w), height=as.numeric(input$h))
                plot(rnorm(sample(100:1000,1)))
                dev.off()
            }
            plot(rnorm(sample(100:1000,1)))
        })

        output$myplot <- renderPlot({ plotInput() })
        output$pdflink <- downloadHandler(
            filename <- "myplot.pdf",
            content <- function(file) {
                file.copy("plot.pdf", file)
            }
        )
    }
)

ui.R

require(shiny)
pageWithSidebar(
    headerPanel("Output to PDF"),
    sidebarPanel(
        checkboxInput('returnpdf', 'output pdf?', FALSE),
        conditionalPanel(
            condition = "input.returnpdf == true",
            strong("PDF size (inches):"),
            sliderInput(inputId="w", label = "width:", min=3, max=20, value=8, width=100, ticks=F),
            sliderInput(inputId="h", label = "height:", min=3, max=20, value=6, width=100, ticks=F),
            br(),
            downloadLink('pdflink')
        )
    ),
    mainPanel({ mainPanel(plotOutput("myplot")) })
)

http://stackoverflow.com/questions/27276994/outputting-shiny-non-ggplot-plot-to-pdf