Answer:
All of the files are stored on a hard-drive. Except for the files you just viewed before turning off the computer, which is stored in the RAM (Random Access Memory). If your computer is a desktop, and the power goes out while looking at a photo/pdf, you may corrupt/lose the image if the computer didn't have enough time to store it in the hard drive. Everything in the hard drive is 'scratched' into it like a record. If you delete a file, that part of the disk is 'smoothed' as best as it can. If you upload another file, you might corrupt/ruin the image/pdf. Think of the smoothing like recording a football game over an old VHS of Winne the Pooh. If you have any other questions, please ask by commenting on this answer!
