How Sendpaper renders files as images in the viewer (and why it matters) | Sendpaper

When you upload a document (like a PDF) to Sendpaper and open it in the viewer, we don’t always stream the original file byte-for-byte to the browser. Instead, we often convert the file into page images and render those images in the UI.

This guide explains:

• what “file-to-images” conversion means
• why the UI shows a loader while conversion runs
• what types of documents are visible in the viewer
• what to expect (and what to do) if a file can’t be rendered

What “convert file to images” means

At a high level, conversion takes an uploaded file and produces:

• one image per page (e.g. page-1.png, page-2.png, …)
• viewer metadata (page count, dimensions) so the UI can lay out pages correctly

Once pages exist as images, the viewer can load them quickly and consistently, regardless of the original file’s internal structure.

Why we use page images in the viewer

Converting to images is a pragmatic choice for a modern document viewer:

• Consistent rendering: pages look the same across browsers and devices.
• Fast initial load: the viewer can show the first page as soon as it’s ready (and keep fetching next pages).
• Better UX for long documents: progressive, page-based loading tends to feel faster than “wait for the whole file”.
• Viewer controls work reliably: page navigation, zoom, thumbnails, and analytics are naturally page-oriented.

Why you see a loader (and what happens during it)

Conversion is server-side work that can take a moment, especially for large files or documents with many pages.

When the viewer shows a loader, it typically means:

• the file was uploaded successfully
• conversion has started (or is queued)
• the viewer is waiting for the first pages (or required metadata) to become available

Once the first pages are ready, the viewer can transition from the loader to the document display and continue loading additional pages in the background.

In-document search on top of page images

File-to-images conversion works together with in-document text search. Once pages are rendered as images, we can still index the text layer so viewers can search inside the document without leaving the secure viewer.

The clip below shows page-by-page analytics and in-document search in action:

In-document search is not a standard feature in most link-tracking or basic document-sharing tools. Most competitors do not provide in-document search inside a secure, page-based viewer, or only in a limited way.

What document types are visible in the UI?

In Sendpaper, “visible in the UI” means: we can render the content as pages in the browser viewer.

Commonly viewable content includes:

• PDFs (most workflows)
• image files (single-page documents like PNG/JPG)

Other document formats may be supported depending on how your workspace is configured and what upload pipeline is enabled. If a format isn’t supported, you’ll typically see an error state instead of the page viewer.

If you’re unsure which formats your setup supports, a safe rule is: if it can be reliably turned into pages, it can be shown in the viewer.

What “processing” means (in plain language)

“Processing” isn’t just a generic spinner; it’s the product doing real work so the viewer can render pages:

• analyzing the file structure
• generating page images
• preparing page sizes and counts for smooth layout

This is why the loader experience matters: it’s the bridge between “uploaded” and “ready to view”.

Practical tips for a smoother experience

• Keep PDFs optimized: very large scans or extremely high DPI pages can take longer to process.
• Expect first-page-first: it’s normal to see the first page before every page is fully ready.
• If a file fails to render: try exporting to PDF and uploading again (it’s the most portable format for page-based viewing).

Summary

Sendpaper converts uploaded files (especially PDFs) into page images so the viewer can render reliably, load progressively, and provide a page-based experience. On top of that, in-document search and page-by-page analytics make long documents actually usable. While conversion runs, the UI shows a loader; once the first pages are ready, the viewer can display the document and continue loading the rest.