PDF Best Practices and Troubleshooting

If a PDF you've uploaded appears blank, loads partially, or fails to render on some devices while working fine on others, it's almost always related to how the PDF was created or exported — not a bug in the file itself. This article explains the most common causes and how to avoid them.

Why This Happens

Our platform renders PDFs using a browser-based viewer. This type of viewer is fast and lightweight, but it has stricter limits than desktop PDF readers like Adobe Acrobat. Two issues account for the vast majority of blank-page reports:

1. Oversized images on a page

If a PDF page is built from a single large raster image (common with scanned documents, exported slides, or design tools like Canva/Photoshop), the viewer may silently fail to render it if the image exceeds a safe pixel-count threshold — roughly 4 megapixels per image. When this happens, there's no error message; the page simply appears empty.

2. Scanner-specific JPEG encoding

Some scanners (for example, certain EPSON models) save pages as JPEGs using a "restart interval" marker — a technical detail in how the image data is chunked internally. This is valid JPEG, and desktop readers handle it fine, but some browser-based viewers fail to decode it and show a blank page instead.

A less common third cause is a PDF with non-integer (fractional) page dimensions — for example, a page sized 540.37 × 860.13 pt instead of clean values. This can trigger boundary errors in some conversion or rendering pipelines.

Best Practices Before Uploading

• Keep images under ~2 megapixels per page when a page is a single flattened image (e.g., 1400×1050 or similar). This leaves comfortable headroom below the ~4MP failure point.
• Export images as JPEG, not raw/uncompressed bitmaps. Uncompressed page images are unnecessarily large and slower to decode; JPEG at a reasonable quality setting looks identical in practice and loads far more reliably.
• Avoid "scan to PDF" defaults. If a document comes from a scanner, re-save or re-export it — for example, by opening it in Adobe Acrobat Reader and using "Save As" — rather than uploading the scanner's raw output directly. This strips scanner-specific encoding quirks.
• Use standard, integer page sizes (A4, Letter, or clean custom dimensions) rather than exporting from tools that produce fractional page boundaries.
• Avoid unnecessary alpha/transparency layers on flattened images — a fully opaque page doesn't need an alpha channel, and removing it reduces file size without any visual change.
• Avoid internal and external links inside the PDF. Links (to other pages in the document, other files, or external websites) are typically blocked by the platform for security reasons and won't work for learners. Keep referenced content as plain text or embed it directly instead of linking to it.
• Keep the file to 100 pages or fewer. Files beyond this limit are not supported. If your document is longer, split it into multiple PDFs.

If a PDF Is Already Showing Blank Pages

1. Confirm it's a rendering issue, not a corrupted file. The PDF usually opens fine in Adobe Acrobat or a desktop viewer — this confirms the file itself is structurally valid.
2. Re-export the file using the guidelines above: resize/compress oversized images, and re-save through a standard PDF tool rather than uploading a raw scan.
3. If the problem persists, share the file with support so we can inspect the underlying image encoding and page structure directly.

Quick Reference

Still stuck? Reach out to support with the affected file attached, and we'll take a closer look.