The iPad doesn’t allow you to copy files to it, like you would a portable drive. Instead, you have to either use iCloud Drive or email documents to yourself.
Add Keynote or PowerPoint Presentations via iCloud Drive
The easiest way to get Keynote or PowerPoint presentations on your iPad is to use iCloud Drive. For Keynote, save the presentation in the designated Keynote folder on your iCloud Drive.
All of the files in that folder will automatically sync on your iPad after you open the Keynote app. Alternatively, you can also copy the file to a WebDAV server or a supported cloud drive like Google Drive. Note, you will need to have the cloud drive app installed on your computer before Keynote will be able to access it.
To get the presentation file from a WebDAV connection, tap on the New button and click on Copy from WebDAV.
To get the presentation file from Google Drive, tap on the New button and then tap on More. Enable and tap on Google Drive.
PowerPoint for iPad has similar options as Keynote. You can save and open files from iCloud and Google Drive. It also supports Microsoft’s OneDrive and Sharepoint servers.
Email Keynote or PowerPoint Presentation
Simply email the presentation to yourself, and then run the iPad’s Mail app. You can then download the presentation inside the message.
Once the iPad finishes downloading the presentation, click on it to open it. By default, it will open it in Preview mode. However, if you have Keynote for iPad installed, it will provide you with the option to open it in Keynote. Click the Share button and then find and tap on the Keynote icon.
It will then import and open the presentation in Keynote.
To save space, you will want to go back to the Mail app, and then delete the message so you don’t have two copies of your Keynote files on your iPad.