Pdf文件不会加载到我的应用程序上

Question

package com.example.bm.kuriotetsuya.pdfviewer;

    import android.support.v7.app.AppCompatActivity;   
    import android.os.Bundle;

    import com.github.barteksc.pdfviewer.PDFView;

    public class MainActivity extends AppCompatActivity {
        PDFView pdf;

        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            pdf= (PDFView) findViewById(R.id.tvpdf);
            pdf.fromAsset("oki.pdf").load();
        } }