Error: Type PdfViewerComponent is part of the declarations of 2 modules

Try the following:

app.module.ts
Leave the import of PdfViewerComponent and add the component in imports: []:

...
FormsModule,
IonicStorageModule.forRoot(),
PipesModule,
PdfViewerComponent 
],
... 

both pages
Remove importation and declaration for both page modules, but add new importation in top of page1.page.ts and page2.page.ts. Then use as you would use before.