If you can see words on the page, but text search isn't finding any words, you either have a raster based PDF, which means the drawing you see is just an image instead of individual lines and letters, or the file could have been created in a CAD program using fonts that are not TrueType fonts so they are not being recognized as letters on the PDF page. You can fix this by running Optical Character Recognition (OCR) on the page or an entire set of drawings.
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