I've no idea why you have received downvotes for a perfectly valid question. Broadly speaking:
Hermoso - Beautiful / Handsome.
Bonito - Pretty / Nice.
Lindo - Cute / Lovely.
But really they are all potential synonyms and often they will be interchangeable with only minor change in meaning. SpanishDict even offers this as one of its definitions:
Tienes un perro lindo - You have a cute dog.
Please, don't ask them to fix anything from this forum, it's only the forum with other users like you here, to help each other about grammar. It's not the place to ask them things, they won't read them here.
Also, I hear "perro", there's no "d" here, so I guess you need training because the English sounds and the Spanish sounds are not the same. Learning a foreign language takes a lot of ear training.
I've heard that to avoid the word, Spanish often uses "perro" for a female dog (just as we do in English). If this is the case, which form of article and adjective is used? Masculine to match "perro" or feminine to match the gender of the dog? I'm guessing masculine should be used?
It's the same in many language. B*tch in English is a female dog, and it's also an insult, in French too, it's not good if you apply "chienne" to a woman.
If you talk about an animals, it's okay.
It's not okay, if you don't talk about animals.
It's the same with the female cat, in English (p*ssy), and in French (chatte), it refers to slang word for private anatomical parts.
You can use "perro" for a female too, if you talk about dogs in general.
For the generality, a kind of neutral, the masculine can be used, in Romance languages, it's the same in French for instance.
A dog of unspecified gender (or we don't care about the gender) = un perro.
But if you want to be precise, it's better and more logical to use = una perra.
Because the Spanish "b" and "v" are pronounced the same, but neither is exactly like the English "b" or "v."
The hard b/v sound is close to our "b" and comes when the letter is at the start of a sentence of follows m/n.
The soft b/v sound is closer to our "v" and is used in all other situations.
For a close approximation of proper Spanish pronunciation make the English sound "b" for hard b/v or "v" for soft b/v, but relax your lips.
There's a good article on it HERE
No. "Pretty" in English is both an adjective and an adverb. "Bonito" is just an adjective.
To say "pretty" cool, fun etc. you need a suitable Spanish adverb. There are a few choices, but the most common are "muy" or "bastante". Use "muy" to say "pretty" in the sense of "very". Use "bastante" to say "pretty" in the sense of "not bad / OK".
So you could say, "Es muy genial" - "It's pretty [very] cool", or "Es bastante divertido" - "It's pretty [not bad] fun".
DL allows typos, which I reckon is generous of them considering a typo is still a mistake. I know of other apps that demand not only accurate spelling, but also correct accent marks.
What DL doesn't allow is typos that make incorrect but legitimate words. "Pero", of course, means "but", which would make your sentence invalid. It is also a noun meaning "fault", which would make your sentence valid, but still incorrect.