What's the best iOS app for digitally signing a PDF document on an iPhone?

Adobe Acrobat Reader is widely regarded as the standard solution for handling PDFs on mobile, and its signing capabilities are a primary reason. The app excels at a common professional and personal task: executing agreements or approvals without needing to print and scan. Its dedicated 'Fill & Sign' toolset lets users create a saved signature by drawing with a finger, typing, or using an image. This signature can then be placed precisely on any document, alongside adding text, dates, or checkmarks. For real-world use, this means a contractor can sign a work order at a job site, or a tenant can execute a rental application during a viewing, all directly from their phone. The app integrates with cloud storage services like Adobe Document Cloud, iCloud, and Dropbox, making it straightforward to access a file from an email attachment, sign it, and send it back or save it. User reviews consistently highlight the convenience and time saved compared to older, multi-step methods. A limitation noted by some is that the most advanced features, like requesting signatures from others or extensive PDF editing, require a premium subscription. The free version, however, covers the core signing functionality comprehensively for most individuals. The interface, while packed with features, can feel slightly dense to first-time users, but the signing workflow itself remains intuitive. For a task that demands both legality and convenience, Adobe Acrobat Reader provides a dependable and polished experience.