Monica de Leon

If they have an older version of Studio than Trados Studio 2021 SR1 CU7 (you have SR1 CU8) then it's because they didn't take steps to ensure it was included, either in purpose or because they simply don't know.  In earlier versions you need to make sure the slider is set to ensure the source file is embedded with the sdlxliff file when you create your project:

In later versions if the embedded settings isn't large enough, or the file is too large even when the setting is 100Mb, the source file will automatically be included in the project.  In the older ones the project manager will need to send you the source file separately if it's not embedded.

Paul I have the contrary issue with version 2021. I do not want the source file to be included, because they are too big (over 300MB each, so the package is 725 MB in size. I removed manually the source files from the project package and its size is now 1.5 MB. But the vendor is not able to open the package due to lack of those files.

How to proceed with this situation?

Sotir Rangelov 

Try sending the target sdlxliff files alone.  Then just replace them in your project when you get the files back.  If you are happy to send a package without the source files anyway then working off the raw sdlxliff files should be fine.

The project package contains also TM and TB. Thus the vendor has to create the project on their own from scratch which may lead to other issues.
As the size limit option is not working, I am sending the package through file transfer service now.

And thank you for your quick reply. :)

Sotir Rangelov 

You could also just zip the project.  Add a folder for the TM and TB inside the project folder, select them so they are correctly linked, then zip the project.  Send the zip to your translator (without the source files).

Seems to me you should start using Language Cloud!!

Yes, this is also a good option. Thank you!