To select only files with no extension use a file mask *.
https://winscp.net/eng/docs/file_mask#exceptions

To change file extension use an operation mask *.bak
https://winscp.net/eng/docs/operation_mask

The command wold be like:

get /source/path/*. C:\destination\path\*.bak

Can you help me with the following problem.
On SFTP server I have files without extension and files with extension .eoj.
For example "filename" and "filename.eoj".
Files with extension .eoj are always empty and they indicate that the file with same name can be transferred.
I have to transfer only files without extension.
After transfer I have to add an extension .bak on file I have been transferred.
How can I do this thing?