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AI Search Gap: Supported MIME Types for embedding files #810

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AI Search Gap: Supported MIME Types for embedding files
dessyordanova Sep 4, 2026
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YoanKar Sep 9, 2026
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31 changes: 28 additions & 3 deletions libraries/radpdfprocessing/features/embedded-file-streams/embedded-file-streams.md
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Expand Up @@ -50,9 +50,34 @@ RadPdfProcessing allows you to embed file streams into the document. The content
|Minimum Version|Q1 2026|
|----|----|

RadPdfProcessing allows you to set the correct MIME type when embedding the file into the PDF. This is especially important for standards like PDF/A-3 and Factur-X, which require strict metadata and MIME type declarations for embedded files.

**Set the MIME Type**
RadPdfProcessing allows you to set the MIME type when embedding a file into a PDF document via the `MimeType` property of `EmbeddedFile`. The `MimeType` property accepts any standard IANA MIME type string. If not explicitly specified, the default value is `"application/octet-stream"`.

Declaring the correct MIME type along with the proper file extension in the `Name` property ensures that PDF viewers (such as Adobe Acrobat) correctly identify the attachment format, associate it with the right host application, and meet requirements for standards like PDF/A-3 and Factur-X.

#### Common Supported MIME Types

The following table lists common MIME types used when embedding attachments:

| File Format | File Extension | MIME Type |
|---|---|---|
| PDF Document | `.pdf` | `application/pdf` |
| OpenXML Word Document | `.docx` | `application/vnd.openxmlformats-officedocument.wordprocessingml.document` |
| Microsoft Word 97–2003 | `.doc` | `application/msword` |
| OpenXML Excel Spreadsheet | `.xlsx` | `application/vnd.openxmlformats-officedocument.spreadsheetml.sheet` |
| Microsoft Excel 97–2003 | `.xls` | `application/vnd.ms-excel` |
| Plain Text | `.txt` | `text/plain` |
| XML Document | `.xml` | `application/xml` or `text/xml` |
| CSV Spreadsheet | `.csv` | `text/csv` |
| PNG Image | `.png` | `image/png` |
| JPEG Image | `.jpg`, `.jpeg` | `image/jpeg` |
| Generic Binary Data (Default) | *any* | `application/octet-stream` |

>important Notice the distinction between Office Open XML formats and legacy binary formats:
>* `.docx` uses `application/vnd.openxmlformats-officedocument.wordprocessingml.document`, while legacy `.doc` uses `application/msword`.
>* `.xlsx` uses `application/vnd.openxmlformats-officedocument.spreadsheetml.sheet`, while legacy `.xls` uses `application/vnd.ms-excel`.
>Assigning `application/msword` to a `.docx` file or omitting the extension in the `Name` property may cause PDF viewers to fail when launching the attachment.

**Example: Embedding Files with Different MIME Types**

<snippet id='pdf-set-mime-type'/>

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