Wait, but the user wants a formula, so maybe present it in a structured way. Like a 5-step daily formula or something. Let's see.

Also, the user might need guidance on where to find materials. Suggesting websites like BBC Learning English, News in Levels, Duolingo (if it's free), and YouTube channels focusing on English learning.

But I need to make sure the steps are doable and free. Maybe the formula is: Read a passage, write a summary, practice grammar, learn new words, and speak aloud. Each part can use free resources.

What's the most effective formula for learning English? It's usually a combination of vocabulary, grammar, and practice. But since the user wants one formula, maybe I can condense it into a daily routine or a specific method.

I should check if there are any common misconceptions about learning English for free. Maybe that it's not effective without paid courses, but the reality is that consistent practice with free resources can be just as good.

I should also mention resources that are free, like online articles, YouTube for listening, free PDFs for grammar, and using Google Docs for writing. Also, maybe include tips on using apps like Quizlet for vocabulary flashcards.

Including a sample PDF structure would help. Maybe a sample study plan and resources list. Also, emphasizing consistency and daily practice is key, even if it's short.

So putting it together, the user is asking for a free PDF that teaches English using one formula or method. The task is to create a text explaining this formula in English, probably for someone who wants to learn English without paying or needing special materials.