This is the 16949th most frequent Russian word.
сопроводительную
"Accompanying" or "supporting."
The word 'сопроводительную' modifies the noun 'форму', describing it as something accompanying the main item, in this case, the application.
Я заполнил сопроводительную форму для заявления.
I filled out the accompanying form for the application.
The word 'сопроводительную' here is used as an adjective to describe the documentation, indicating it accompanies the project.
Мы подготовили сопроводительную документацию для проекта.
We prepared the accompanying documentation for the project.
In this sentence, 'сопроводительную' describes the noun 'записку', showing it serves as an addition accompanying the report.