What do you mean by ‘sending it to another page’?
If you use the file manager (https://docs.mendix.com/refguide/file-manager/) you can upload a file.
This file will be stored as a System.FileDocument entity in your application.
And this entity can be use throughout your app with the retrieve action.
To get more control of the uploaded file, the best practise is to inherit the system.FileDocument into an entity in your own domain model. You can give that entity a unique number (autonumber), or attach it through association with another entity in your domain model. This makes it easier to retrieve the file later.
I hope this helps.