All contracts, invoices, contractual documents in general, estimates, deposit receipts or related documents must be in Catalan. This includes product warranties, adhesion contracts, contracts with standard clauses and regulated contracts (article 128-1 of the Law 22/2010 of the Catalan Consumer Code and article 15 of Act 1/1998 on linguistic policy).
Moreover, invoices and other documents have even more specific obligations for certain sectors. Thus, more concretely, the following kinds of companies, among others, are doubly affected:
There are also various obligations in Andorra:
Contracts, orders, invoices, estimates, receipts and generally speaking all business documentation must be in Catalan (article 22 of the Law regulating the use of the official language, from the year 2000).
As for patents in Andorra, although they can be registered in Catalan, Spanish, French or English, a central part (reivindications, that is, the description of the invention) has to be written in Catalan. In case of infraction, the requests of precautionary measures and evidences have to be written in Catalan too (Law 26/2014 of 30th October, of Patents).
The Government of Catalonia provides templates for different documents in the labour, business, administrative, legal and academic areas that are available to companies that wish to use them. You can see some examples of them at this portal or this one. The Government of Andorra also provides some very useful linguistic resources.