Usually I hear all the acronyms (like ASAP) spelled out, even if reading them like they were a word would be possible. So my question is: is there a formal rule for the pronunciation of acronyms? Or would it be possible to pronounce them like normal words but for the sake of clarity this isn't done?
I'm trying to give you a possible answer based on a 10 minute study on commonly used acronyms. There is no formal rule as such. But based on my personal observations, some acronyms can be read out as if they were actual words. This is usually for acronyms which doesn't sound funny when spoken. An acronym with a vowel, at some position, has a higher chance of being read out as a word. Let us take the acronyms mentioned in the comments (and a few more):
ASAP, SCUBA, LASER, RADAR, SWAT, NASA, FIFA, WHO.
It is pretty clear that the vowels are positioned in favorable places, so as to give an impression that it can be read out as words.
Now if the same acronyms had a vowel removed, (No copyright infringement intended, just to explain), and say they were :
SCBA, LSER, RDAR, SWT, NSA, FFA, WH.
it would sound super weird if we try to read these out as words. Ergo, we end up spelling it out.
Now let us look at a few acronyms with vowels, which are still not pronounced as if they were words:
FBI, ICC, CBI, CFO
In these acronyms, the vowels are not in favorable position so as to give it a 'word-like' structure.
Apart from all these, there are a few acronyms, which can be read out as words, but are not as they sound really odd
USA, DOD, CEO, MIA, MIT
These are some of the acronyms that can be read out as words, but aren't, maybe because it doesn't sound all that appealing.