Fix PDF thumbnail generation – add System.Drawing reference and reset stream position

[mohiuddin-khan-shiam]

Problem

PdfThumbnailProvider could fail at compile-time and/or produce empty or invalid thumbnails at runtime:

1. Image / Bitmap types come from System.Drawing, but the namespace was missing, causing build errors in environments that don’t rely on implicit global usings.
2. After rendering the first PDF page to an in-memory stream, the stream’s cursor remained at the end.
   Image.FromStream(stream.AsStream()) therefore read zero bytes, throwing an exception or creating an empty bitmap.

Fix

• Added explicit using System.Drawing;.
• Added stream.Seek(0); right before Image.FromStream(...) to rewind the stream to the beginning.

using System.Drawing;   // new
...
page.RenderToStreamAsync(...).GetAwaiter().GetResult();
stream.Seek(0);         // rewind so Image.FromStream reads data
imageOfPage = Image.FromStream(stream.AsStream());

Testing

• Rebuilt the solution – compilation succeeds without missing-namespace errors.
• Ran thumbnail handler against multiple PDFs; thumbnails now render correctly and no runtime exceptions are thrown.

Impact

Users regain reliable PDF thumbnail previews in Explorer, improving usability and preventing crashes or blank icons.

[Copilot]

Pull Request Overview

Fixes PDF thumbnail generation by explicitly adding the missing System.Drawing reference and rewinding the in-memory stream before creating the image.

• Added using System.Drawing to resolve missing namespace errors.
• Inserted stream.Seek(0); to reset the stream position so Image.FromStream(...) reads data correctly.

Comments suppressed due to low confidence (1)

src/modules/previewpane/PdfThumbnailProvider/PdfThumbnailProvider.cs:99

• Consider wrapping the stream in a using statement or explicitly disposing it after use to free resources and avoid potential memory leaks.

stream.Seek(0);

[yeelam-gordon]

Thanks for having the change.

[lei9444]

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[lei9444]

/azp run

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