Yes, if it helps you understand the sentences, you can rewrite in the passive form. However, it's worth noting that in business contexts, it is normal to use verbs such as 'sell' and 'trade' as intransitive verbs, with the commodities which are sold and traded as the subject of these verbs. The phrase 'A bond sells..' is correct and appropriate in a business context. That said, what struck me first about this line is the awful punctuation error which comes up twice in the one sentence. Whoever wrote this may know about business, but he or she deserves zero out of ten for punctuation. It should be 'its market price' and 'its par value'. 'It's' is the contraction of 'it has' or 'it is'. The possessive form is 'its' - no apostrophe. The verbs in this sentence are fine. The punctuation is wrong. It makes the writer look ill-educated and unreliable. If I were looking for information about the stock market, I wouldn't go to a source whose writers were ignorant of the basic rules of punctuation.

Yes you can replace the active form of the verbs with the passive but as Su Ki said in business contexts it is quite common to use certain verbs in an active intransitive form even if the subject does not actually 'do' the action. In English we have a number of verbs which can be used in this way. They are called Ergative verbs and can have 3 forms 1. Active transitive: She sells flowers.2. Passive transitive: Flowers are sold everyday at the market 3. Active intransitive ergative: These flowers sell well. Here is a list of English ergative verbs http://en.wiktionary.org/wiki/Category:English_ergative_verbs

"A bond is originally sold for $1000, then is traded up to $1100. Now it's market price is $1,100, but it's par value remains $1000."