MAC OS desktop application

I have windows a windows application which I need for MAC OS. I have attached the Windows Demo Video and also explained the process. [login to view URL] Application Process : I upload 100 images to my website and send the link to my friend and he select 50 among those 100 .jpg image files. As soon as he select the file and click finalize I receive .txt file to my mail which is encrypted by Base64 algoritham (The purpose of Encryption is that only our application read that file names) Here the application Part: The application should get the .txt document and decrypted .txt document and move the list of file (selected 50 images in the .txt file ) from the "100 images folder" to the "Selected" folder. It should also have the options to change the .Jpg extensions because the image may be in .NEF format which is nikon RAW format or some Dslr camera formats, the only way to upload in web is to convert to .jpg that the reason we I ask for change extension. If Ineed to Sort the .NEF files (File names wiill be same) in can that the extension