files app removing files and not opening

PDF files i were previously able to open on my files app won’t open anymore. only the ones in my icloud. the files labelled “on my iPad” will not open if they are PDF. i tried pressing quicklook to try bypass a glitch or lag but it completely erased my file, it’s not even in recently deleted it’s just gone. this is very frustrating as these are my uni notes with so much information on markup. i need help. i don’t have enough space to backup up the rest, im scared to turn off icloud incase it deletes my files on my ipad