By 'local space' I meant that each app is totally isolated from every other app. In Windows programs/apps can communicate directly with each other. So you could download a file with Internet Explorer and then switch to, say, Word and open that file from within Word. You can't do that on the iPad. When you download a file using, say, Safari (and Safari can only download certain types of files) that file resides solely in the Safari file space. It cannot be accessed by another app directly. So, if you downloaded a PDF file and then switched to a PDF app you wouldn't be able to 'see' that file because it would be isolated within the Safari domain.
To be able to get, say, iBooks to read it you use the 'Open In' facility that iOS provides. From within Safari, if you select the PDF downloaded iOS will offer 'Open In' and a list of programs that can process the PDF file. When you select one, say iBooks, a *copy* of the file is made by iOS into the iBooks filespace. So now there are two entirely separate copies of that PDF file that are completely independent. If you, say, deleted the Safari copy, the iBooks' copy would still be left.
Tim