sudo zypper search convertall- did not find anything because you do not have configured any repository containing convertall.
Previous poster suggested that convertall lives in ..../Kde:Extra repository. You will need to add that repository for your openSuSE version, refresh repositories and then you should be able to successfully search and install convertall.
While there are other ways to go about searching for application not included in default repositories - I propose this:
1. Always check your current repositories: sudo zypper search convertall
Or even better, using Yast
That did not work for you as explained above.
Search in all distributions for convertall
3. If the seach found the package for your version of openSuSE in experimental or community packages - click "1 Click Install" to add relevant repository and install the package.
This way, the package should install all dependencies and will be automatically updated when you update your computer.
If there is equal choice between experimental and community packages - I would recommend that you choose experimental as it is maintained by openSuSE. So there is probably better chance of getting help.
That being said, investing into good openSuSE knowledge foundation by using manuals, as suggested before me, is the best way to become competent user.
Good luck,
Tomas