- textbook → educational book
"Search" could be look for, investigate, explore. "Online repositories" might be digital archives, web databases, virtual storage. "Websites" could be sites, portals, platforms. "Like" in this context, maybe similar to, resembling. "Academia.edu" and "ResearchGate" are proper nouns, so no synonyms. "Online libraries" could be digital libraries, web-based libraries, internet libraries. "Copy" might be instance, version, exemplar. "Available" could be obtainable, accessible, present. Aula Internacional 1 Pdf Free Download-
Similarly for other words.
"Purchase the textbook" can be "Acquire the book," "Buy the manual," or "Obtain the workbook." Obtain the workbook. - textbook → educational book "Search" could be
Inspect Internet platforms: Some web sites, similar to Google Books or Amazon, may supply some free glimpse nor sample from that textbook. "Like" in this context, maybe similar to, resembling
I need to be careful with phrases like "step-by-step guide" and replace each component. "Step-by-step" could be "procedural|gradual|methodical". "guide" as "resource|manual|instruction".