To preface: I have both iOS 11 and macOS High Sierra. My friend was using a Windows machine. From the Files app with iOS 11, I just emailed a friend a folder that consists of pdf files that I stored in iCloud drive over a year ago. The friend informed me that some of the files in the folder were not able to be opened, while other files were able to be opened. I resent the same folder from my Mac and she said the same issue occurred again. She then sent me a picture which showed that the pdf files that were not able to be opened ended in .pdf.icloud rather than .pdf From iCloud Drive, I noticed that the files that my friend was having trouble opening (.pdf.icloud) were all not downloaded to my iPhone and/or Mac from iCloud (and instead showed the iCloud icon). I downloaded the entire folder then sent the folder containing the pdf files and my friend was then able to open all of the files. I have never experienced this before, so I was unsure if this was a bug for iCloud Drive in iOS 11 and macOS High Sierra, or if you always had to download the folder before sending to someone else. Any input would be greatly appreciated. Thanks.