Pdf result different with Aperçu and Acrobat

I create some documents with Pages converted in "pdf" mode to be sent to a printing office. Last year the result was perfect, this year a little bit less, particularly the shadow of typefaces is pixelated as the result when the file is read with the native Apple reader is perfectly smooth. I discovered that the same file read with Acrobat Reader provides a much less smooth result. Does anyone has an explanation and a solution to correct the problem because most professional printing systems function under Adobe software.

Regards