That's not right. The Pocketbook Touch still uses *.dic dictionaries. Copy them into the folder /system/dictionaries/ of your Pocketbook 622.
.pbi is a download file, it stands for something like pocketbook installation file. Pocketbook uses them to distribute commercial dictionaries and the language packages. I don't think that there is a possibility for us users to convert from dic to pbi.
Welcome to MR, Michel