A PDF up to 25 MiB with up to 40 pages can be turned into a single tall PNG with PDF to Long Image, provided the final canvas stays within 12,000 pixels per side and 100 megapixels total. The converter stacks every page from top to bottom into one continuous vertical image, which is useful when a chat, social platform, slide review session, or archival workflow expects one picture instead of a multi-page document. Large files run into the tool's hard safety limits before they run out of disk space: source documents above 25 MiB or 40 pages are rejected, individual rendered pages above 12,000 pixels per side or 40 megapixels are rejected, and the combined tall canvas is rejected if it exceeds 12,000 pixels per side or 100 megapixels. Because the long image grows with the number of pages, even modest PDFs can hit the final canvas ceiling. The tool preflights every page and the full combined layout before it starts encoding, so the exact combined width, height, and page count are known before a single pixel is written.
What "large file" means to this converter
For a normal image converter, a large file might mean anything over a few megabytes. For PDF to Long Image, "large" is defined by four independent ceilings that all have to pass at the same time: source file size, page count, individual rendered page size, and the size of the final combined canvas. A 20 MiB PDF with five pages can convert without issue; the same 20 MiB PDF with eighty pages is rejected at the page-count gate before any rendering begins. A four-page PDF where each page is 4,000 pixels tall and 3,000 pixels wide can also be rejected, even though it is small in megabytes, because the long canvas would stretch past the 12,000-pixel height ceiling. Understanding these gates up front is the difference between a one-shot conversion and an error message.
Hard limits for the long image
The converter enforces a fixed set of limits so a runaway document does not exhaust your browser's memory or produce an unusable picture. Every limit is checked during a preflight pass before encoding starts, and any failure aborts the job cleanly.
| Limit | Maximum | What it controls |
|---|---|---|
| Source PDF size | 25 MiB | The local PDF you select |
| Page count | 40 pages | How many pages are stacked |
| Per-page dimensions | 12,000 pixels per side | One rendered page before it is drawn into the canvas |
| Per-page pixel count | 40 megapixels | Total pixels in one rendered page |
| Combined canvas dimensions | 12,000 pixels per side | Width and height of the final tall PNG |
| Combined canvas pixel count | 100 megapixels | Total pixels in the final tall PNG |
The combined canvas limits are the ones that bite hardest on large files. Doubling the rendering scale quadruples the pixel count of every page, so a document that fits comfortably at a low scale may blow past the 100-megapixel ceiling at a higher scale even when the page count is small.
Convert a large PDF to one long image
The flow is the same for a small PDF and a 25 MiB one, but large files benefit from choosing a lower scale up front so the final canvas stays inside the limits.
- Open PDF to Long Image and choose one PDF up to 25 MiB from your device.
- Pick a rendering scale and a gap between pages from 0 to 32 pixels. For large files, start at the lowest scale that still looks readable rather than the maximum.
- Press Convert to Long PNG. The tool loads the PDF, runs the page-by-page preflight, and reports the combined width, height, and page count.
- Confirm that the combined dimensions fit within 12,000 pixels per side and 100 megapixels. If they do not, lower the scale and reconvert.
- Download the single tall PNG. The filename is the input name minus the .pdf suffix, with unsafe characters replaced, ending in -long.png.
Choosing scale and gap for big documents
Scale is the single biggest lever for large files. The total height of the final canvas is the sum of every scaled page's height plus the gaps between them. For a 40-page document with zero gap, that sum is page count × per-page height. If each page renders to 250 pixels tall, the final canvas reaches 40 × 250 = 10,000 pixels, which fits under the 12,000-pixel ceiling. Raising the scale to 500 pixels per page pushes the total to 40 × 500 = 20,000 pixels, well past the limit. The page gap is a smaller secondary lever: a 32-pixel gap on a 40-page document adds (40 − 1) × 32 = 1,248 pixels to the total. At low scale the gap is invisible; at high scale it can be the difference between fitting inside the canvas and hitting the ceiling.
Why the final image is sometimes too tall
A document can pass the per-page checks and still fail the combined canvas check. This happens whenever page count times the scaled page height exceeds the 12,000-pixel height limit, or whenever the total pixel count exceeds 100 megapixels. Long slide decks, scanned books, and any PDF with many similarly sized pages are the usual culprits. The error is reported before any PNG is written, so a half-finished file is never produced. Reducing scale or trimming the document with Split PDF before converting are the two reliable fixes.
What the long PNG keeps and discards
The long image is a rendering, not a structural conversion. PDF.js paints the visible content of every page — text, vector artwork, photographs, fonts, and clipping paths — onto a canvas, and the converter then draws those canvases onto one combined canvas. Selectable text, live links, form controls, editable annotations, layers, document metadata, and the original embedded images are not preserved in the output. The widest rendered page sets the canvas width, and narrower pages are centered horizontally without being stretched. The gap area and any side margins are white, and the final encoding is explicit lossless image/png.
If your file is too large for one long image
When a document cannot fit inside the limits, the cleanest fallback is to render pages individually. PDF To PNG produces one lossless PNG per page with no height limit on any single page beyond the per-page ceilings, which is a better fit for scanned books or long reports. For a smaller file size per page at the cost of some quality, PDF to JPG Converter renders each page as a JPEG. If the goal is one picture but the document is genuinely too tall, splitting the source PDF with Split PDF and stacking the resulting long images side by side in a second tool is the standard path.
The original PDF is never modified. Whatever you do not convert stays exactly as it was, and the long PNG is a separate file you can share, archive, or delete on its own.
Related reading: Convert a Large PDF to PNG Without Uploading It.