Hi Chaz2460,
welcome to the Apple (user-to-user) Community
Re: "IPad files app and storage of full page PDF screenshots"
Try looking in the "Recently Deleted" folder in the Files App, to see if you can recover the PDF files:
How to recover the Files if you find them:
Delete a file or recover a file that you deleted from the Files app - Apple Support
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Wondering if you have enough free storage for the screenshots, and also for your iPad to operate smoothly:
How to check the storage on your iPhone and iPad - Apple Support
How to make space using recommendations:
If you need more space for an update on your iPhone, iPad, or iPod touch - Apple Support
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If still not finding the screenshot PDF files:
How to:Find files on your iPhone or iPad in the Files app - Apple Support
Also:
You may want to check in the Books App
Read PDF documents in Books on iPad - Apple Support
Save and edit PDFs to the Books app on your iPhone or iPad - Apple Support
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If needed: How to: Restore your iPhone, iPad, or iPod touch from a backup - Apple Support
or
How to: Restore all content to iPad from a backup – Apple Support
All the best :-)