E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.textscannerandconverter, PID: 3777
    java.lang.IllegalStateException: document is closed!
        at android.graphics.pdf.PdfDocument.throwIfClosed(PdfDocument.java:225)
        at android.graphics.pdf.PdfDocument.writeTo(PdfDocument.java:170)
        at com.example.textscannerandconverter.TextRecognition$7.onClick(TextRecognition.java:290)
        at android.support.v7.app.AlertController$ButtonHandler.handleMessage(AlertController.java:167)
        at android.os.Handler.dispatchMessage(Handler.java:105)
        at android.os.Looper.loop(Looper.java:156)
        at android.app.ActivityThread.main(ActivityThread.java:6523)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:942)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:832)