Philip Sundt 

Retrofit is of no use here since you don't have the original project. It's also not the best solution for this anyway.

Given you only have an updated source, and an old target file alignment would be the way to go.  But before you do that have you got all the translations in your TM?  If you have then just create a new project with the updated source file, pre-translate it from your TM, complete the bits that won't be translated as they are the updated parts, and save the target file.

If for some reason you didn't save the previous job to a TM then align the source and target.  Create a TM from it and then use that as the TM to translate the updated source file with in a new project with the updated source file.  Complete the bits that won't be translated as they are the updated parts, and save the target file.

Philip Sundt 

Retrofit is of no use here since you don't have the original project. It's also not the best solution for this anyway.

Given you only have an updated source, and an old target file alignment would be the way to go.  But before you do that have you got all the translations in your TM?  If you have then just create a new project with the updated source file, pre-translate it from your TM, complete the bits that won't be translated as they are the updated parts, and save the target file.

If for some reason you didn't save the previous job to a TM then align the source and target.  Create a TM from it and then use that as the TM to translate the updated source file with in a new project with the updated source file.  Complete the bits that won't be translated as they are the updated parts, and save the target file.

Thank you Paul! I did save the original translation in a TM. I'll see if I can pre-translate the new file from the TM, and otherwise do the file alignment.
Again, many thanks!