Загрузите pdf файл на сервер и получите его URL

Полный рабочий пример, протестирован для файлов размером более 100 Мб, замените your_package с вашим именем пакета.

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"package="your_package" >

<uses-permission android:name="android.permission.INTERNET"/>

<application
android:allowBackup="true"android:icon="@mipmap/ic_launcher"android:label="@string/app_name"android:theme="@style/AppTheme" >
<activity
android:name=".MainActivity"android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />

<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>

Макет activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"android:layout_width="match_parent"android:layout_height="match_parent">

<Button
android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="Browse"android:id="@+id/browse"/>

<Button
android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="Upload"android:id="@+id/upload"/>
</LinearLayout>

Деятельность MainActivity

package your_package;

import android.app.ProgressDialog;
import android.content.Context;
import android.content.Intent;
import android.net.Uri;
import android.os.AsyncTask;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;

public class MainActivity extends AppCompatActivity {
Uri path;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

Button browse = (Button) findViewById(R.id.browse);
Button upload = (Button) findViewById(R.id.upload);

browse.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
Intent intent = new Intent();
intent.setType("application/pdf");
intent.setAction(Intent.ACTION_GET_CONTENT);
startActivityForResult(Intent.createChooser(intent, "Select PDF"), 1);
}
});
upload.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
(new Upload(MainActivity.this, path)).execute();

}
});
}

public void onActivityResult(int requestCode, int resultCode, Intent result) {
if (resultCode == RESULT_OK) {
if (requestCode == 1) {
path = result.getData();
}
}
}
}

class Upload extends AsyncTask<Void, Void, Void> {
private ProgressDialog pd;
private Context c;
private Uri path;

public Upload(Context c, Uri path) {
this.c = c;
this.path = path;
}

@Override
protected void onPreExecute() {
super.onPreExecute();
pd = ProgressDialog.show(c, "Uploading", "Please Wait");
}

@Override
protected void onPostExecute(Void result) {
super.onPostExecute(result);
pd.dismiss();
}

@Override
protected Void doInBackground(Void... params) {
String url_path = "http://192.168.43.50/projectpri/upload.php";
HttpURLConnection conn = null;

int maxBufferSize = 1024;
try {
URL url = new URL(url_path);
conn = (HttpURLConnection) url.openConnection();
conn.setDoOutput(true);
conn.setUseCaches(false);
conn.setDoInput(true);
conn.setChunkedStreamingMode(1024);
conn.setRequestMethod("POST");
conn.setRequestProperty("Connection", "Keep-Alive");
conn.setRequestProperty("Content-Type", "multipart/form-data");

OutputStream outputStream = conn.getOutputStream();
InputStream inputStream = c.getContentResolver().openInputStream(path);

int bytesAvailable = inputStream.available();
int bufferSize = Math.min(bytesAvailable, maxBufferSize);
byte[] buffer = new byte[bufferSize];

int bytesRead;
while ((bytesRead = inputStream.read(buffer, 0, bufferSize)) != -1) {
outputStream.write(buffer, 0, bytesRead);
}
outputStream.flush();
inputStream.close();

BufferedReader reader = new BufferedReader(new InputStreamReader(
conn.getInputStream()));
String line;
while ((line = reader.readLine()) != null) {
Log.i("result", line);
}
reader.close();
conn.disconnect();
} catch (Exception e) {
e.printStackTrace();
}
finally {
if (conn != null) {
conn.disconnect();
}
}
return null;
}
}

PHP на стороне сервера

$file_name = date("U").".pdf"; //name of your file
$server_path = "/path/to/file/folder/"; //server path to folder
$web_path = "http://192.168.43.50/projectpri/file/"; //web path to folder

$file = $server_path.$file_name;
file_put_contents($file,"");

$fp = fopen("php://input", 'r');
while ($buffer =  fread($fp, 8192)) {
file_put_contents($file,$buffer,FILE_APPEND | LOCK_EX);
}

echo $web_path.$file_name;