#1 Your sentences are not wrong. I would omit "as the" from both sentences to use "attached" as an adjective. As a noun, "attached" can be used like this: Please find the relevant information IN the attached. #2 I don't understand these sentences. I think when you say "if it happens" that you mean it is happening to YOU. This is not clear, but assuming this is what you mean, Here are some possible ways to express this idea: "If I should (ever) happen to buy this book, I will also buy this." "If I (should) ever happen to eat this food, I would throw up." #3 Use subjunctive mood for "receive": "I'm pushing (on) the vendor so that he receive the product as soon as possible." (I used "he" instead of "I" to make it clear how subjunctive mood works. With "he", you say "receive", not "receives") Your last sentence is perfect.

#1 I’m attaching the file. Please find the reference information as the attached. #2 Your examples are incorrect and the intended meaning of your examples are unclear. A correct example: If it happens to rain, I’ll be prepared. (Similar to ‘if it rains’ but reinforces the idea that rain is uncertain. ) #3 Your examples are good and natural