Cyril Carraz This is most likely because 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 relogin to the studio to check if additional pages are processed. The same applies to analyze operation too. Thanks!!
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