Reading business documents and contracts:[1]

Laymen documents, such as loan, business, collateral, and accounting documents, and the like of matters which are forbidden to be done on Shabbos, are forbidden to be read on Shabbos due to the decree of “Mimtzoe Cheftzecha”.

Reading them in ones thought without verbalizing: Furthermore even to read in ones thought without verbalizing [the words] is forbidden.

The reason why even in thought it is forbidden: It was only said that speech is forbidden while thought is permitted when it is not evident [to others] that one is thinking about forbidden matters. However here that it is evident to all that one is thinking of the forbidden matters which are written in the document, it is thus included in the prohibition of “Mimtzoe Cheftzacha” just as was included in this [decree against] one who is strolling in his field to see what it requires. As although strolling in a field is a permitted matter in it of itself, as well as thinking about the needs of one’s field is a permitted matter, nevertheless since it is apparent to all that he is strolling there for this purpose, it is therefore forbidden due to “Mimtzoe Cheftzecha”, as was written in chapter 306 [Halacha 1-2].

Summary:

It is forbidden to read, whether verbally or in one’s mind,  business documents such as loans, contracts and all matters of the like which are forbidden to be done on Shabbos. This is due to the decree of Mimtzo Cheftzecha, which one is not to do weekday activity on Shabbos.