文档广告只允许推广无访问门槛的文档，例如文献、幻灯片或电子书。

This statement is incorrect because Document Ads on LinkedIn can promote documents that require a download or have an access gate, such as lead generation forms. While they are excellent for sharing open-access content like whitepapers or presentations, they also serve as a powerful tool for capturing leads by requiring users to provide information to access the document. The platform allows advertisers to gate content, making it a versatile format for both awareness and lead generation campaigns.