Documents\Public location

The methods you need are under BRApi.Filesystem:

• BRApi.FileSystem.GetFile
  BRApi.FileSystem.InsertOrUpdateFile
• BRApi.FileSystem.GetFileShareFolder

Here's a mock example that just copies a file from a user's document folder and changes the name.  You'll need to swap the sourceFile/sourceDir pieces with FileShare pieces from BRApi.FileSystem.GetFileShareFolder according to your needs.

'Source file
Dim sourceFile As String = "SomeCSV.csv"
Dim sourceDir As String = $"Documents/Users/{StringHelper.RemoveInvalidNameCharacters(si.UserName,False,False)}"
'Target File
Dim targetFile As String = "CopiedFile.csv"
Dim targetDir As String = sourceDir
				
'Get the file
Dim sourceXFFileEx As New XFFileEx
sourceXFFileEx = BRApi.FileSystem.GetFile(si, FileSystemLocation.ApplicationDatabase, sourceDir & "/" & sourceFile,True,True)
												
'Save the file				
Dim targetFileDataInfo As New XFFileInfo(FileSystemLocation.ApplicationDatabase, targetFile, targetDir)
Dim targetFileData As New XFFile(targetFileDataInfo, String.Empty, sourceXFFileEx.XFFile.ContentFileBytes)
BRApi.FileSystem.InsertOrUpdateFile(si, targetFileData)