Paths can be relative, such as ". \file.txt". To resolve such a path and display its full path, you could use Resolve-Path:
PS> Resolve-Path .\file.txt
Unfortunately, though, Resolve-Path expects the file to really exist, so you cannot use it on hypothetical paths. To resolve all paths, whether they exist or not, use this line instead:
PS> $ExecutionContext.SessionState.Path.GetUnresolvedProviderPathFromPSPath('.\file.txt')
