The Challenge

A fast-growing SaaS company approached Sulonya with a recurring problem: their users needed a reliable way to collaborate on large PDF files and able to redact the PDF file.

The documents were not simple 2-3 page files but contracts, reports, and manuals often exceeding 200 pages. Every time, the platform struggled:

• Documents were slow to load or crashed the viewer entirely.

• Adding annotations such as comments, highlights, drawings, or e-signatures introduced severe lag.

• Annotations often appeared inconsistently across collaborators, causing miscommunication and lost edits.

User frustration was growing, support tickets were mounting, and adoption of the client’s platform was stalling. For the client, fixing this was not just a feature enhancement - it was critical for customer trust and product success.

Our Solution

Sulonya’s engineering team understood that performance patches would not be enough. The entire architecture needed to be rethought for scalability, reliability, and collaboration.

MVP on redaction of the PDF

Before deep diving into the project issues (which we knew we could resolve) we wanted to figure out a way to redact a PDF and thus provided an MVP within 2 weeks to showcase our technical prowess.

Performance-First with Lazy Loading

Instead of loading the entire PDF at once, we built a lazy loading engine:

• Only visible pages were processed in real time.

• Background preloading ensured navigation remained instant.

• Memory usage was reduced by more than 70 percent, even on large documents.

Optimized Annotation Layer

We designed a lightweight annotation system that supported highlights, comments, freehand drawings, and digital signatures, with a focus on responsiveness. The result was a lag-free editing experience regardless of file size.

Real-Time Synchronization

To ensure consistency in collaboration, we implemented a real-time sync engine:

• All users saw the same set of annotations.

• Conflict resolution logic handled simultaneous edits.

• Edits were preserved reliably across sessions.

Enterprise-Grade Reliability

Given the client’s enterprise user base, we also built in:

• Robust error handling to eliminate crashes.

• Security measures for handling sensitive documents.

• A scalable framework capable of supporting thousands of concurrent users.

The Impact

The solution delivered measurable improvements:

• Smooth navigation and editing, even on 200+ page PDFs.

• Consistent, real-time collaboration across distributed teams.

• A significant reduction in support tickets, easing pressure on customer support.

Renewed enterprise trust in the platform, driving higher adoption and retention.

What was once the client’s most problematic feature became a competitive differentiator, directly contributing to product growth.

Client Feedback

Our users went from calling PDF collaboration unusable to saying it is the smoothest part of our product. What Sulonya delivered wasn’t just performance - it restored user trust. That has been invaluable.

                              - Product Manager, SaaS Client

Key Takeaway

• Great engineering is not just about fixing what is broken. It is about anticipating scale, ensuring reliability, and creating experiences that users trust.

• This project demonstrates how rethinking performance and collaboration at the architectural level can turn a bottleneck into a growth driver.

• Contact Us to learn how Sulonya can help solve your toughest engineering challenges.