Try to set the
the default open behavior for the site collection or document library based on your requirements as the following.
To Set the default open behavior for site collections as the following:
- In the SharePoint site collection, choose the Settings icon > Site Settings.
- On the Site Settings page, under Site Collection Administration, choose Site Collection Features.
- On the Features page, for the Open Documents in Client Applications by Default feature, choose Activate to enable the OpenInClient feature (documents will open in the client application), or Deactivate to disable the OpenInClient feature (documents will open in the browser).
To Set the default open behavior for a document library by using the document library settings page:
- On the document library page, choose the Library tab.
- In the Settings group, choose Library Settings.
- On the Document Library Settings page, choose Advanced settings.
- On the Advanced Settings page, in Opening Document in the Browser, select
Open in the browser from the following options:
Open in the client application When a user chooses a document in this library, the document will open in the corresponding client application if it's available.
Open in the browser When a user chooses a document in this library, the document will open in the web browser in the web app for that document type.
Use the server default When a user chooses a document in this library, the document will open by using the default open behavior specified for the server running SharePoint 2013.
If the issue still exists please review the configuration of Office Web Apps as mentioned at Use Office Web Apps with SharePoint 2013. So in this case,
For more details check Set the default open behavior for browser-enabled documents (Office Web Apps when used with SharePoint 2013)