There is more than one option.
Leave the File Open on your office computer.
Use a different copy of FileMaker Pro (cannot have the same install code) to access the file via Open Remote.
Use FileMaker Go on your iPad to access the file.
With both iPad and your lap top, you have to set up port forwarding on your office internet router to forward requests to your office computer. You'll need to connect to the IP address of your router, not your office computer. Some details on setting up Port Forwarding are specific to your internet router so you'll need to research this.
Configure your office computer to permit remote desktop access. From your laptop, you can then use this form of access to select and open any file on your computer--including your database. Don't think this works for an iPad.
Set your file up with Instant Web Publishing. Then use a web browser on either lap top or iPad to access the database. This limits your user interface features and still requires port forwarding to be set up, but you no longer need FileMaker Pro on your lap top nor do you need Filemaker Go on your iPad.