Jun Zeng The most likely reason that you are seeing only the first two pages being analyzed is that you are using a resource which is on the free tier. This is documented on the limits and custom model pages of the documentation.
For PDF and TIFF files, up to 2,000 pages can be processed. With a free tier subscription, only the first two pages are processed.
Please update the pricing tier to standard or S0 from Azure portal and then re-login to the studio to check if additional pages are processed. The same applies to training operations too. Thanks!!
I have recently answered as similar query from another user who had an additional question after upgrading to S0 tier, you can refer this thread for more information if you have similar query.
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