Most file conversions cost 1 credit per file to process but larger files might cost more. The number of credits required for a skill is previewed in the app before you run it.
Once you have run a skill or conversion, you will also see exactly how many credits were used. The amount will be charged from your Filestar account. If the file conversion was unsuccessful, no credits will be charged. If the conversion requires more credits than you have you will get a notification about that in the application and asked to visit our Pricing page to load up on more credits.