I got a warning on my Xperia L4 there not enough storage space and some apps may not work. I deleted some files and now have 5GB free of 64GB. Is that considered enough free space?
I don’t know if there is a connection but some pdfs open very slowly and it take a while to display anything except white blank pages. Even when reading and scrolling down sometimes the next page may be blank and take a few seconds to display the content. It may be a problem with the pdf as it does not happen all the time
For light/general use that is probably enough space. That model phone has a slot for SD card (supposedly upto 512GB), they are pretty cheap these days so you could add more space easily enough.
If the pdfs in question are purchased ebooks as your other thread suggests (and other pdfs without encryption or DRM open a lot faster), the delay might not be so much in opening, as decrypting and/or verifying DRM-wise that you do indeed have permission to view its content. Adding storage space unfortunately won’t help with that.
That’s up to your Android, it usually starts complaining at some percentage of space, eg. less that 5%
Note that 64Gb is total system space, some of it (10-20Gb?) is used by “system” and you can’t actually use it for your pics or apps. (check that in Android - Settings - Storage I guess)