If you are Using InDesign, you can enable the pinch zoom on pdf files. Kindly try the following steps :
- Extract all the pages from the PDF as single PDF pages.
- Open InDesign - make a new document with correct amount of pages, your PDF had, make 2 layers, named '-background' and 'layer 2'.
- 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.
- Repeat this whole process until you have the whole pdf in your in your InDesign file.
- Save your document.
- 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.