extract text layer from searchable pdf and merge with another pdf

[Lutrin]

Dear comp.text.pdfians

I have a pdf (a searchable pdf consisting in book pages scans, then passed
to ocr that has added a text layer hidden under images, so pdf is
searchable)

this pdf has jbig2 compression (it counts 135 pages in A5 format scanned
at 300 dpi and its size is about 1928 KB)

After ocrization, I noticed that scans have been degrated in quality, so I
want extract text layer and merge this text layer with another copy of
same pdf containing scans in high quality

it is possible extract a text layer from a pdf and then merge with raster
layer of another pdf?
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