Ok, I got it working!
One last question...when I was testing locally, the files created in the "www" folder remained after the session ended. Do I need to add a few lines of code to clear out any *.pdf files from the "www" folder when the session ends or will they get cleared automatically?
test_result_path <- file_temp("test_result_pdf", tmp_dir = "www", ext = ".pdf")
output$test_results <- renderUI({
test_result() %>%
str_replace("https://s3.amazonaws.com", "s3:/") %>%
get_object() %>%
writeBin(test_result_path)
tags$iframe(style = "height:1400px; width:100%", src = str_sub(test_result_path, 5))
})