Obsidian needs files to be stored on the device to be able to work with them. Cloud services sometimes store only placeholders on the device and download the actual file when you open it. If pCloud does that, look for a setting that forces it to keep the files on the device.
Or maybe you need to grant some kind of permissions, or connect pCloud to your file manager or something?
If all else fails you might try the Remotely Save plugin, which synchronizes with cloud services that Obsidian is otherwise unable to use.