**Complex Sentence:**

After examining carefully the reports from all sources, I was able to gather comprehensive information on the subject matter.

**Explanation:**

In the given sentence, the original sentence is a simple sentence as it consists of only one independent clause. To make it a complex sentence, we need to add a dependent clause to provide more information or context to the main clause.

1. **Identify the Independent Clause:**

The independent clause in the original sentence is: "I examined carefully the reports from all sources."

2. **Add a Dependent Clause:**

To make it a complex sentence, we can add a dependent clause at the beginning or at the end of the independent clause. Let's add the dependent clause at the beginning:

"After examining carefully the reports from all sources,"

3. **Combine the Clauses:**

Now, we need to combine the dependent clause with the independent clause to form the complex sentence:

"After examining carefully the reports from all sources, I was able to gather comprehensive information on the subject matter."

This new sentence consists of a dependent clause "After examining carefully the reports from all sources," and an independent clause "I was able to gather comprehensive information on the subject matter." The dependent clause provides additional information about the action of examining the reports, adding more context to the sentence.

By creating a complex sentence, we have expanded on the original sentence and provided a clearer understanding of the situation. The addition of the dependent clause helps to explain the purpose or outcome of examining the reports, showcasing a more comprehensive analysis.