dependencies:
  pdf_flutter: ^version

    <key>io.flutter.embedded_views_preview</key>
    <true/>

    PDF.network(
            'https://raw.githubusercontent.com/FlutterInThai/Dart-for-Flutter-Sheet-cheet/master/Dart-for-Flutter-Cheat-Sheet.pdf',
            height: 500,
            width: 300,
            maxAndroidZoom: widget.maxAndroidZoom,
            midAndroidZoom: widget.midAndroidZoom,
            minAndroidZoom: widget.minAndroidZoom,
    )

    File fileName;  
    PDF.file(
        fileName,
        height: 200,
        width: 100,
        maxAndroidZoom: widget.maxAndroidZoom,
        midAndroidZoom: widget.midAndroidZoom,
        minAndroidZoom: widget.minAndroidZoom,
    )

    PDF.assets(
        "assets/pdf/demo.pdf",
        height: 200,
        width: 100,
        maxAndroidZoom: widget.maxAndroidZoom,
        midAndroidZoom: widget.midAndroidZoom,
        minAndroidZoom: widget.minAndroidZoom,
    )

Here are the steps to fix:
    1. Add proguard-rules.pro file if its not already there

    2. Inside of the proguard-rules.pro file put this:
        -keep class com.shockwave.**
        -keepclassmembers class com.shockwave.** { *; }
        
    3.In app/build.gradle add this:

        shrinkResources true
        minifyEnabled true
        proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'