Whenever you save your work in Tableau, the default file extension is .twb, or Tableau Workbook. However, you have the option to save your work under a different extension, .twbx which @Swaroop has already shown in his reply.
A .twbx file is a Tableau Packaged Workbook, meaning it is the original .twb file grouped together with the data source(s) in one package. .twbx files can be considered analogous to specialized zip files, in which these “zip” files contain all the information necessary to work in Tableau. The primary advantage to using .twbx files is that analysis can be performed without network/internet connections to your data because your data is already present on your computer in this packaged file.
The .twb file alone is not enough to perform any analysis because it only contains Tableau’s instructions for interacting with a data source. In actuality, .twb files are XML files specially tailored to interact with data sources.
Hope this will help.
this is probably what your cowork got
a twb file does not include the data - you need to send a TWBX file that has the data included - go to file - extract - then set it as a twbx file
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1. Use the above mentioned approach to send the TWBX file rather than TWB file.
2. Send the dataset as well, so he can edit the connection of that twb workbook.
And, Please do mark this post completed as the above mentioned answer solve your query.