I'm trying to export a PDF from indesign, i've used "knockout group" for making an hole on a solid color rettangle using text. Tried with text at 0% opacity, or white text at 100% multiply, and in both cases, when i export pdf it doesen't work unless it is be opened from acrobat. When i try to send it by whatapp the solid color rettangle il filled at 100% without showing the background trought the text (as if there was no text).
How can i solve it?
You'll have to do it a different way. 3rd party PDF readers may not be able to render the effects properly... that's a limitation of the app you're using, not InDesign. If you're not talking about a lot of text, I would use the approach of Converting your text to Outlines, then use Pathfinder to Subtract it from your colour box. the drawback is you won't be able to edit your text without going through the process again, but it'll work.
Just a thing to try: when you save your PDF, select 1.3 Compatbility. Since your effects are Level 3 effects that are truly meant for high-end ouput, if you select 1.3, it will flatten the heck out of it and maybe dumb it down for other Readers. Let me know!
Thanks @roaringmousegraphics, effectively 1.3 compatibily works for cutting text from the solid and for now is the best solution for me because i'm still finishing this project and i use PDF just like preview (for now, but in the future it will be used to make an app) sending it by whatapp (my customer doesn't even know how to power on a PC, imagine download acrobat reader), but now the stroke of the text box (there is no stroke on the setting) create a cutting over the solid too. Suggestion?
Exporting PDF 1.3 Compatbility allows "knockout group" also in others pdf viewer but, as showed in previous post, it cut the stroke of textbox, but (as @Eugene Tyson suggests) it can be solved using a white fill on bottom of the layer and page (i've used 100% multiply because there is a background on the mastro) with solid rectangle.
I totally agree with @roaringmousegraphics. PDF readers other than Adobe Acrobat or Reader are not designed for print workflows. They simply were not designed read more complex constructs like a knockout group, and many other effects.
WhatsApp? That's not a reliable PDF reader, unfortunately, only Acrobat is a real PDF reader as they are the creators of PDF.
Any other PDF reader that is not Adobe is in fact a 3rd party PDF reader and don't use all the PDF modules.
What's happening is that WhatsApp is not supporting transparency in the PDF that's why it's not working.
If you have to send through Whats App you might have better luck with a JPEG or something else.
The last thing I can suggest is to put a white background underneath - using a White fill for the whole page.
And then export the using the PDFx1a setting.
It might work.