diff --git a/app/src/main/AndroidManifest.xml b/app/src/main/AndroidManifest.xml
index 3712e15ad..c708341f8 100644
--- a/app/src/main/AndroidManifest.xml
+++ b/app/src/main/AndroidManifest.xml
@@ -35,4 +35,12 @@
         </provider>
     </application>
 
+    <queries>
+        <!-- Intent query to open PDF files -->
+        <intent>
+            <action android:name="android.intent.action.VIEW" />
+            <data android:mimeType="application/pdf" />
+        </intent>
+    </queries>
+
 </manifest>
diff --git a/app/src/main/kotlin/edu/stanford/bdh/engagehf/messages/HealthSummaryService.kt b/app/src/main/kotlin/edu/stanford/bdh/engagehf/messages/HealthSummaryService.kt
index ed84519b6..988df5b6f 100644
--- a/app/src/main/kotlin/edu/stanford/bdh/engagehf/messages/HealthSummaryService.kt
+++ b/app/src/main/kotlin/edu/stanford/bdh/engagehf/messages/HealthSummaryService.kt
@@ -2,9 +2,9 @@ package edu.stanford.bdh.engagehf.messages
 
 import android.content.Context
 import android.content.Intent
-import android.os.Environment
 import androidx.core.content.FileProvider
 import dagger.hilt.android.qualifiers.ApplicationContext
+import edu.stanford.bdh.engagehf.R
 import edu.stanford.spezi.core.coroutines.di.Dispatching
 import edu.stanford.spezi.core.logging.speziLogger
 import edu.stanford.spezi.core.utils.MessageNotifier
@@ -31,21 +31,25 @@ class HealthSummaryService @Inject constructor(
                     "${context.packageName}.provider",
                     savePdfToFile
                 )
-                Intent(Intent.ACTION_VIEW).run {
+                val pdfIntent = Intent(Intent.ACTION_VIEW).apply {
                     addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION)
                     addFlags(Intent.FLAG_ACTIVITY_NEW_TASK)
                     setDataAndType(pdfUri, MIME_TYPE_PDF)
-                    context.startActivity(this)
+                }
+                if (pdfIntent.resolveActivity(context.packageManager) == null) {
+                    messageNotifier.notify(messageId = R.string.no_pdf_reader_app_installed_error_message)
+                } else {
+                    context.startActivity(pdfIntent)
                 }
             }.onFailure {
-                messageNotifier.notify("Failed to generate Health Summary")
+                messageNotifier.notify(messageId = R.string.health_summary_generate_error_message)
             }
     }
 
     private fun savePdfToFile(pdfBytes: ByteArray): File {
         logger.i { "PDF size: ${pdfBytes.size}" }
-        val storageDir =
-            Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS)
+
+        val storageDir = context.getExternalFilesDir(null) ?: context.filesDir
         if (!storageDir.exists()) {
             storageDir.mkdirs()
         }
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index 46fc54299..0399e4cf4 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -122,4 +122,6 @@
     <string name="dizziness_score_title">Dizziness Score</string>
     <string name="dizziness_score_description">Your dizziness is important to keep track of because dizziness can be a side effect of your heart or your heart medicines.</string>
     <string name="error_while_handling_message_action">Error while handling message action.</string>
+    <string name="no_pdf_reader_app_installed_error_message">Health Summary generated successfully, but no PDF reader is installed on the device</string>
+    <string name="health_summary_generate_error_message">Failed to generate Health Summary</string>
 </resources>
diff --git a/core/utils/build.gradle.kts b/core/utils/build.gradle.kts
index ea20b01da..7139dbe61 100644
--- a/core/utils/build.gradle.kts
+++ b/core/utils/build.gradle.kts
@@ -7,6 +7,10 @@ plugins {
 
 android {
     namespace = "edu.stanford.spezi.utils"
+
+    defaultConfig {
+        testInstrumentationRunner = "edu.stanford.spezi.core.utils.HiltApplicationTestRunner"
+    }
 }
 
 dependencies {
@@ -16,4 +20,5 @@ dependencies {
     implementation(libs.kotlinx.serialization.json)
 
     testImplementation(libs.bundles.unit.testing)
+    androidTestImplementation(libs.bundles.unit.testing)
 }
diff --git a/core/utils/src/androidTest/kotlin/edu/stanford/spezi/core/utils/HiltApplicationTestRunner.kt b/core/utils/src/androidTest/kotlin/edu/stanford/spezi/core/utils/HiltApplicationTestRunner.kt
new file mode 100644
index 000000000..2464d6baa
--- /dev/null
+++ b/core/utils/src/androidTest/kotlin/edu/stanford/spezi/core/utils/HiltApplicationTestRunner.kt
@@ -0,0 +1,13 @@
+package edu.stanford.spezi.core.utils
+
+import android.app.Application
+import android.content.Context
+import androidx.test.runner.AndroidJUnitRunner
+import dagger.hilt.android.testing.HiltTestApplication
+
+@Suppress("Unused")
+class HiltApplicationTestRunner : AndroidJUnitRunner() {
+    override fun newApplication(cl: ClassLoader?, className: String?, context: Context?): Application {
+        return super.newApplication(cl, HiltTestApplication::class.java.name, context)
+    }
+}
diff --git a/core/utils/src/androidTest/kotlin/edu/stanford/spezi/core/utils/MessageNotifierTest.kt b/core/utils/src/androidTest/kotlin/edu/stanford/spezi/core/utils/MessageNotifierTest.kt
new file mode 100644
index 000000000..fffaf4274
--- /dev/null
+++ b/core/utils/src/androidTest/kotlin/edu/stanford/spezi/core/utils/MessageNotifierTest.kt
@@ -0,0 +1,38 @@
+package edu.stanford.spezi.core.utils
+
+import androidx.test.platform.app.InstrumentationRegistry
+import dagger.hilt.android.testing.HiltAndroidRule
+import dagger.hilt.android.testing.HiltAndroidTest
+import kotlinx.coroutines.test.StandardTestDispatcher
+import kotlinx.coroutines.test.runTest
+import org.junit.Before
+import org.junit.Rule
+import org.junit.Test
+import javax.inject.Inject
+
+@HiltAndroidTest
+class MessageNotifierTest {
+
+    @get:Rule(order = 1)
+    val hiltRule = HiltAndroidRule(this)
+
+    @Inject
+    lateinit var messageNotifier: MessageNotifier
+
+    @Before
+    fun init() {
+        hiltRule.inject()
+    }
+
+    @Test
+    fun `it should not fail when toasting in main thread`() {
+        InstrumentationRegistry.getInstrumentation().runOnMainSync {
+            messageNotifier.notify("Some message")
+        }
+    }
+
+    @Test
+    fun `it should not fail when notifying on a background thread`() = runTest(StandardTestDispatcher()) {
+        messageNotifier.notify("Some message")
+    }
+}
diff --git a/core/utils/src/main/kotlin/edu/stanford/spezi/core/utils/MessageNotifier.kt b/core/utils/src/main/kotlin/edu/stanford/spezi/core/utils/MessageNotifier.kt
index 3b83ba4c5..ad7c1da00 100644
--- a/core/utils/src/main/kotlin/edu/stanford/spezi/core/utils/MessageNotifier.kt
+++ b/core/utils/src/main/kotlin/edu/stanford/spezi/core/utils/MessageNotifier.kt
@@ -1,6 +1,8 @@
 package edu.stanford.spezi.core.utils
 
 import android.content.Context
+import android.os.Handler
+import android.os.Looper
 import android.widget.Toast
 import androidx.annotation.StringRes
 import dagger.hilt.android.qualifiers.ApplicationContext
@@ -9,9 +11,15 @@ import javax.inject.Inject
 class MessageNotifier @Inject constructor(
     @ApplicationContext private val context: Context,
 ) {
+    private val mainHandler by lazy { Handler(Looper.getMainLooper()) }
 
     fun notify(message: String, duration: Duration = Duration.SHORT) {
-        Toast.makeText(context, message, duration.value).show()
+        val toast = { Toast.makeText(context, message, duration.value).show() }
+        if (Looper.myLooper() == Looper.getMainLooper()) {
+            toast()
+        } else {
+            mainHandler.post { toast() }
+        }
     }
 
     fun notify(@StringRes messageId: Int, duration: Duration = Duration.SHORT) {