As described, you may have a display fault/screen backlight failure. Hopefully you will have had the foresight, as is good practice, in having an iCloud or iTunes backup - this being your insurance policy should the unexpected occur such as technical failure, or loss/theft of a device.
If your data and documents are important to you, always have a backup - as sooner or later, something will happen that leads to to data loss, this being true of any computing device.
If you don’t have a backup, the opportunity to preserve your locally stored data may have been lost. If your iPad is repaired, all locally stored data will be unavoidably erased. If you do have a backup, other than some inconvenience, you should be able to restore your data to your iPad after repair - or to a replacement iPad.
It is perhaps possible, in very bright ambient light, to see the screen - at least sufficiently to enter your Passcode and access some settings, or to respond to on-screen prompts. If so, you may be able to backup your iPad to a Windows PC (with iTunes for Windows installed) or a Mac computer (with iTunes or Finder - as appropriate for the installed version of macOS).
Alternatively, you may be able to enable an iCloud backup - assuming that you have adequate iCloud storage space. You can subscribe to additional iCloud+ storage if you need to - paid storage tiers being 50GB, 200GB and 2TB
The available methods to backup your iPad are described here:
How to back up your iPhone, iPad, and iPod touch - Apple Support
If you intend to use iCloud - and need more storage:
Upgrade to iCloud+ - Apple Support
iCloud+ plans and pricing - Apple Support
If using iCloud for the backup, connect your iPad to its Power Adapter - ideally close to your WiFi Router so as to ensure that you have a good WiFi connection.
Assuming that you can see the iPad screen sufficiently (using an external light source if necessary), for an iCloud backup to be enabled, these are the settings that you must access:
Settings > [Your Name / AppleID] > iCloud > iCloud Backup >
- Back Up This iPad - set to ON
- Back Up Now
Leave your iPad connected to its Power Adapter while the backup takes place. If you have lot of data, the backup may take a while.
