If you are Using InDesign, you can enable the pinch zoom on pdf files. Kindly try the following steps :

  1. Extract all the pages from the PDF as single PDF pages.

  2. Open InDesign - make a new document with correct amount of pages, your PDF had, make 2 layers, named '-background' and 'layer 2'.

  3. Import the first pdf page, (scale to fit the pdf to the page) in to the -background layer, then copy and paste in place the pdf on to layer 2.

  4. Repeat this whole process until you have the whole pdf in your in your InDesign file.

  5. Save your document.

  6. Export to the App Studio Portal and test the normal way on your device. You should now be able to pinch and zoom your content.