Fix Corrupted Large PDF Uploads to SharePoint via API
Question details
The user needs to resolve an issue where PDF files larger than 4 MB become corrupted when uploaded to SharePoint programmatically via a CRM API.
- Product
- SharePoint API
- Device & OS
- not provided
- Scenario
- Uploading PDF files from a CRM system to SharePoint using an API integration.
- Observed behavior
- PDF files larger than approximately 4 MB become corrupted after API upload, whereas smaller files and manual uploads via the SharePoint interface work correctly.
Before adjusting your API code, manually upload the same large PDF file directly to the SharePoint web interface to confirm the corruption is strictly limited to the API integration rather than an issue with the file itself.
Verify API Chunking and Header Configurations
Ensure the API handles large file transfers correctly by using chunked uploads and accurate content length headers.
SharePoint REST APIs have specific payload limits for single-request uploads. When transferring files over a certain threshold (often around 4 MB), a standard upload request may truncate the file, leading to corruption.
To resolve this, large files must be uploaded using chunking methods, which break the file into smaller pieces and reassemble them on the server.
Check your CRM's integration documentation or the SharePoint REST API guides to ensure you are using the correct endpoint for large files (e.g., CreateUploadSession or StartUpload/ContinueUpload/FinishUpload).
Analyze your API request headers to ensure the Content-Length exactly matches the binary payload size of the PDF being transmitted.
If your integration already sends files in chunks, confirm that the byte offsets and sequences are accurately calculated so the final PDF is properly assembled without missing data.
Compare File Checksums and Review Recent Updates
Identify if the file is being modified in transit by comparing checksums and auditing recent system updates.
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Frequently Asked Questions
Why do only PDFs larger than 4 MB get corrupted via API?
Many APIs and middleware gateways have default buffer limits or single-request payload limits (often around 2 MB to 4 MB). Files exceeding this require chunked uploads; if the integration attempts a single upload, the payload may be truncated, resulting in a corrupted PDF.
How can I test if the issue is with SharePoint or the CRM API?
Attempt to manually upload the exact same large PDF file directly through the SharePoint web interface. If the manual upload succeeds and the file opens correctly, the issue is isolated to the API upload method or CRM integration.
What SharePoint REST API endpoint should be used for large files?
For files larger than a few megabytes, it is recommended to use the Microsoft Graph API's `createUploadSession` or the SharePoint REST chunked upload endpoints (`StartUpload`, `ContinueUpload`, and `FinishUpload`) rather than the standard `/Files/add` endpoint.
